I believe Jesus when He said “This is My Body”
Paul tells us Jesus felt so strongly about this doctrine He personally taught it to him.
Ignatius tells us the Gnostics did not take the Eucharist because they did not believe it to be the flesh of Jesus Christ. ( it seems the doctrine was “folly” to them )
the question is why you hold to the gnostic belief over Jesus, Paul and Ignatius.
Incorrect. Ignatius as well as Irenaeus disputed with the Gnostics especially as concerning the observance of the Eucharist. The Gnostics didn't believe that Jesus HAD flesh and blood. The Gnostics viewed everything physical as evil. Had Irenaeus argued that the natural elements of common juice and bread were transubstantiated into something different than what they appear, namely the body and blood of Christ, the Gnostics would have agreed completely, while maintaining their view that the body of Christ was not composed of natural elements, but only appeared to be. Had Irenaeus been arguing transubstantiation, the Gnostics would have countered, "We agree and it proves Jesus did not have literal flesh and blood. Just as you (Irenaeus) have argued that the bread and juice must be transubstantiated into something that is undetectable to our senses, we argue that the reason it is undetectable to our senses, is because the literal body and blood of Christ on the cross, like the bread and juice, were not what they appear!
So it was critical that Irenaeus specifically avoid the doctrine of transubstantiation in his recorded argument against the Gnostics.
The way the church refuted the Gnostics was based upon the symbolic view. As late as 200 AD, Tertullian bases the reality of Christ's body on the cross, upon the fact that the bread is symbolic:
"Taking bread and distributing it to his disciples he made it his own body by saying, "This is my body," that is a "figure of my body." On the other hand, there would not have been a figure unless there was a true body." (Tertullian, Against Marcion IV. 40)