Life is a pissing contest.
Ask Darwin. He called it evolution, because pissing contest seemed a bit rude.
Modern civilisation does it's best to disguise it, but underneath it all, it's still there, and when nations get involved, its the military that does the pissing.
So essentially, the answer to your question "Why do all the threads end up in pissing contests?" is because this is a military forum, and we are the cock, metaphorically speaking........or not metaphorically in the case of the RAF.
Hope that clears it up.