“Somehow they don’t seem to really, truly trust God, and so they have to add to what He did on the cross.”
...and do you trust these words from Jesus?
John 6:53-58, 66-67
“So Jesus said to them, ‘Truly, truly, I say to you, unless you eat the flesh of the Son of man and drink his blood, you have no life in you; he who eats my flesh and drinks my blood has eternal life, and I will raise him up at the last day. For my flesh is food indeed, and my blood is drink indeed. He who eats my flesh and drinks my blood abides in me and I in him. As the living Father sent me, and I live because of the Father, so he who eats me will live because of me. This is the bread which came down from heaven, not such as the fathers ate and died; he who eats this bread will live forever.”
I don't, by the grace of God, make the error of believing "another Christ" can morph bread and wine into the blood and body of Jesus in some sort of wizardly alchemy.
It is enough for me that I am saved by Christ's one-time sacrifice on the cross. Read Hebrews 10.