Most people making arguments for "the other side" haven't actually had to defend them against real criticism. They also are usually not the originators of their position, they're forwarding the ideas from someone else, so they don't necessarily even understand what it is they are articulating.
Trying to engage with someone who doesn't know how to argue and doesn't actually grasp their ideas is about as productive as trying to argue with a 4-chan meme. I've long ago decided to just put my 2-cents in a single time, if I feel they're saying something really stupid, then move on.