Here's why: we have a situation where, for once, we've landed on the same conclusion. We got there for different reasons. Instead of looking at that as a great opportunity to learn something new from our differing perspectives, it's something that somehow manages to piss you off. If political discussion doesn't work here, it's certainly not going to work anywhere else.
I'm not getting my wish that discussions like these simply be banned from the site, but maybe we could take a baby step towards civility by not calling people names.