Correction: Attacking other Christians just because of the church one attends simply does not further the cause for Christ and the Gospel.
I think the attacks are due (other than just normal anti catholic feelings) to the fact that the Magisterium and Catechism are readily available so they can look for things that don’t suit their feelings. It’s pretty much impossible to go back at them since there are 10,000 (at least) different ideas of protestantism. I really get tired of the constant criticism of Msgr Pope, etc by the armchair theologians.