I would say it's politics. The only threads that get contentious are the political ones, the others run for a long time and everyone is happy and polite, then Tom comes in and gives away something nice to someone who has a need. I think he's bribing us to hang out with him.
Elsewhere on the 'net, folks seem to think gun forums are there to inject politics into nearly every discussion. If it isn't overtly politics, then there will be snide references to "libtards" or whatever politician has managed to get their attention (and will be referred to in as derogatory way as their little brains can conjure).
Pretty much, especially if your firearms interest is narrowly focused like many here (not a critique, just an observation).
Personally, I "contribute" more to the non-gun or non-pistol-training stuff because I don't know enough about pistol-training and pistol-related excellence to to anything other than absorb from everyone else who is knowledgeable. Other gun forums don't even have that much going for them.
Chris