It is funny that irl, I never come across Orthodox or Catholics that are anywhere close to as venomous as those this board.
Two things-- First, one difference here is that people in real life usually keep nasty stuff to themselves, or keep it to a select few they trust share similar views; while people on the internet are more open about blurting things out (so to speak). Are people on the internet more a--holish, or more honest? Or both? Second, one other factor that might be at play here is that people on a board like this are generally going to be passionate about this kinda stuff. That's why they're here.
So, let's say you talk to 100 Orthodox/Catholics in real life, and no one says anything nasty about contraception or Baptists or atonement theory. Maybe 10 of them think you're a disgusting heretic for believing x, y and z, but just wait till they get home before crap-talking you. The other 90 simply don't care, they're more interested in how the donuts taste (which is a more normal mindset). Yet, cross them regarding something that does
interest them, and I bet their would indeed be nastiness, in their head at the very least.