Gnosticism vs. The Church
"spirit=good, body=bad." Therefore, if the item under consideration is related in some way to the physical- material world , it is earthy, wordly and can't be spiritual and good. Based on that, Catholicism had to be wrong because of its very visible presence. Furthermore, all of the sacraments were "hinged"* on material objects. Water for baptism, oil for confirmation, bread and wine for the Eucharist.
Unfortunately, this false paradigm undermines the very tenets of Catholicism. The Incarnation itself shows us how this construct is wrong. The Church was started to be a visible vehicle for conveying God's grace. God physically entered the world in the flesh, and the Church He established should mirror this principle. Jesus was never meant to be separated from the Church, His grace was always intended to flow through the sacraments, not separate from them as mere symbols. Read this post here on Principium Unitatis for an excellent discussion on gnosticism and the Church.
*Tertullian said "flesh is the hinge of salvation."