Well, except for when they don’t:
While within Gnosticism you had the belief that Christ only looked corporeal but was not (matter being held as evil), in Catholicism you have the belief that (in transubstantiation) the body and blood of the crucified Christ only looks, feels, tastes and would test as non-corporeal, as bread and wine, but is not. And even that these elements no longer actually exist despite their appearance and provable, testable properties (and even though these elements can decay, at which point the body and blood of Christ no longer exist as them). Thus the lack of such Biblical proofs of the real body and blood of Christ, nor the evidence to the contrary, do not matter here, and are treated as deception.
The issue here is not that God could not perform the novel miracle of transubstantiation, but besides the possibility of particles being airborne and thus God ending up in the carpet, etc., and of organic decay being continuous (thus Christ ceasing to exist in the hosts before being eaten), the problem is that the Catholic interpretation of the words of the Lord's Supper and the discourse on the bread of life in John 6 is contrary to both a plain literal interpretation of them, which Catholics often assert they hold to, and to how the body and blood which Christ refers to was really "present" in His incarnation. And thus to the evidential warrant God provides for faith in the Christ of Scripture.
For as John teaches (in contrast to the Christ of certain Gnostics), that "Christ is come in the flesh" is true in the light of His manifest physicality, "That which was from the beginning, which we have heard, which we have seen with our eyes, which we have looked upon, and our hands have handled, of the Word of life," (1 John 1:1) "This is he that came by water and blood, even Jesus Christ; not by water only, but by water and blood. And it is the Spirit that beareth witness, because the Spirit is truth." (1 John 5:6)
And the words said at the Last supper which Catholics claim to take literally say that this body was the body that would be "broken for you," (1Co. 11:24) "my flesh, which I will give for the life of the world," Jn. 6:51) and the blood that would be "shed for you." (Lk. 22:20) And which certainly looked, felt, smelled, and would taste like and scientifically test as literally being real flesh and blood. And which I think also would the body that Thomas was invited to touch as proof that Christ arose, (Jn. 20:27) though He can materialize appear at will.
While we are to believe on Christ by faith now, the Christ we believe on is one whose incarnated body was manifest as being so — its appearance corresponded to its reality — and appeared bodily even in His resurrected state. In contrast, worshiping a Christ that looked like, felt like, smelled like, and would taste and scientifically test as an inanimate object — and in multiple locations, at the same time — would be worshiping a false Christ. Anyone could say that an inanimate object was God, and imagine the apostles trying to preach that a loaf of bread was really Christ!
Trent says, "Because Christ our Redeemer said that it was truly his body that he was offering under the species of bread [actually after breaking bread He said "this is my" body"]... by the consecration of the bread and wine there takes place a change of the whole substance of the bread into the substance of the body of Christ our Lord and of the whole substance of the wine into the substance of his blood, (Trent, 1376) if not in any evidential, or provable way.
However, at the Last supper the Lord did not say anything like "this bread is changed into my body," or that the bread "becomes" it, while if the apostles could believe in transubstantiation, then the same souls could certainly have believed that what they consumed at the Last supper was the same manifest flesh and blood that would be on the cross. That would be 100% literal and easier than requiring belief in a novel miracle that relies on specious Neoplatonic thought and Aristotelian metaphysics to explain.
The only problem is that Catholic priests cannot come up with the same manifestly incarnated body and blood that was crucified, (purported "Eucharistic miracles" are contrary to the doctrine of transubstantiation), thus instead we have the Catholic "real" body and blood of Christ" that does not correspond (in the ways Christ was manifestly incarnated) to the real incarnated Jesus which a literal reading of the texts at issue speak of.
While within Gnosticism you had the belief that Christ only looked corporeal but was not (matter being held as evil), in Catholicism you have the belief that (in transubstantiation) the body and blood of the crucified Christ only looks, feels, tastes and would test as non-corporeal, as bread and wine, but is not. And even that these elements no longer actually exist despite their appearance and provable, testable properties (and even though these elements can decay, at which point the body and blood of Christ no longer exist as them). Thus the lack of such Biblical proofs of the real body and blood of Christ, nor the evidence to the contrary, do not matter here, and are treated as deception.
In other words, they are claiming that the bread and wine are really the body and blood of Christ — being present whole and entire in His physical "reality," corporeally present...", (Mysterium Fidei) even down to subatomic particles (until they begin to decay) — which is what He said would be crucified. And they present a Eucharistic Christ as being same sacrifice as at Calvary, yet they deny that it is physical in the ways that proved Christ was incarnated and the ways define physical. but which does not physically belong to this universe as He did when He was crucified.
Anyone could say Christ was an inanimate object but this Catholic Christ this is not what the apostles and NT church preached, nor as being the gospel, nor of the Lord's supper. Instead, in preaching His life, death resurrection and reality they they invoked His manifest physicality. by whom "God was manifest in the flesh." (1Tim. 3:16) When invoking proofs for the resurrection, it was that Christ was actually seen by multitudes, not that He appeared as a piece of bread. The Lord's supper was said to proclaim His death, (1Co. 11:26) not manifest Christ, and the church is called "one bread" and the body that believers needed to discern.
Yet in Catholicism believing that the bread and wine is the very body and blood of Christ is a required belief. Not only must Catholics believe that the incarnated Christ who so identified with us that He manifestly became man and manifestly felt our pain now identifies Himself as a wafer of bread (but does not feel the pain of being eaten), that what they see as a wafer of bread is "the very body which he gave up for us on the cross, the very blood which he "poured out for many for the forgiveness of sins," (CCC 1365) but (whether they realize it or not) consequently they also are to believe the bread and wine no longer exist after the priest utters his words of consecration, "since transubstantiation means the Real Presence of Christ, it also means the real absence of bread and wine. To believe this is to be a Roman Catholic." ( John A. Hardon, S.J., Part I: Eucharistic Doctrine on the Real Presence)
In contrast, the language of "take eat, this is My body" easily conflates with the use of metaphorical language in Scripture, and endocannibalism and drinking blood is forbidden in Scripture, (Lv. 17:10) and that the bread that Christ broke at the Last supper easily represents the Lord's real body that was "bruised [dâkâ'=broken] for our iniquities" and the wine represents the shed blood of the Lord who "poured out his soul unto death." (Isaiah 53:5,10,12) Ps. 22:14 prophetically says, "I am poured out like water, and all my bones are out of joint: my heart is like wax; it is melted in the midst of my bowels."
And in John 6, this "eating" and "drinking" can only represent receiving the words of Christ as food, which is what the Lord said man is to live by, (Mt. 4:4) and conforms to the means of obtaining spiritual life elsewhere in Scripture, and to living by Christ as Christ lived by the Father, (Jn. 6:57) with doing His will therefore being His "meat." (Jn. 4:34)
In addition, Catholics do not take the Lord purely literally when He said to “drink this cup,” for you do not literally drink a cup (though if transubstantiation is allowed, so a means of ingesting a cup could be explained), but it is manifest that the cup represents what it contains, likewise the contents represent what would be visibly shed.
Moreover, in every other miracle which the Lord did that changed something material then there was an obvious tangible change — water really become wine which only existed in that location — versus a change of substance while the appearances remained the same, and so the body of Christ could be sitting at a table before them while being in the stomachs of the disciples.
Therefore, the Catholic understanding of the Lord's supper is both contrary to a purely literal reading of the words at issue, and contrary to how the incarnated and crucified and risen Christ was presented as really "present" body and blood, soul and Divinity" on earth. And preaching inanimate objects as "really" being the Lord Jesus body and blood is that of preaching "another Jesus," and preaching that the Lord's supper is how one obtains spiritual life is that of preaching "another gospel."
But I fear, lest by any means, as the serpent beguiled Eve through his subtilty, so your minds should be corrupted from the simplicity that is in Christ. For if he that cometh preacheth another Jesus, whom we have not preached, or if ye receive another spirit, which ye have not received, or another gospel, which ye have not accepted, ye might well bear with him. (2 Corinthians 11:3-4) ^
Much more by God's grace.