I've thought a lot about this, and I've come to the conclusion that it's a combination of a minimalist approach to religion and a modern day version of gnosticism on the parts of the bashers.
Take a look around this Forum: what are the things about Catholicism that really get the haters wound up? Statues, the Blessed Virgin, rituals, the ceremonial attention paid to the Pope -- all things that the Protestants don't have. They have reduced religion to a mere spiritual exercise and forgotten that Jesus Himself worked with material things.
He used a few fish and some bread to teach the disciples a lesson in faith, just as He used coins in the mouth of another fish to prove a point to Peter. He even spat on the ground and made mud to heal a blind man! There's absolutely nothing wrong with material things and so-called 'pagan' rituals (baptism being one of them, BTW) as long as God has purified them and sanctified them to His use.
And the other problem is that Protestants unconsciously seem to feel that matter is evil -- Gnosticism at its worst. That's why all that they do is symbolic: baptism symbolizes renewal, Communion symbolizes Christ's body and blood. . . symbol after symbol, but nothing real and concrete by way of spiritual benefits.
God never worked that way in the Old or the New Testaments: when He said to do something, there was a very real result that followed. March around the city and blow those trumpets. . .by golly, those walls of Jerico fell down! Bathe seven times in the Jordan -- pfft! There went Naaman's leprosy! Each time, there was a very real benefit to visibly expressing one's faith in God.
The bottom line is that many Protestants are stuck "having a form of godliness, but denying the power thereof." (2 Timothy 3:5) If God chose to be worshipped by physically sacrificing animals and His Son opted to work in material things to increase faith, then I see no problem with the Catholic Church using purified and sanctified physical materials in worship, either.