if you’re planning to kill the guy, what would you do with our cat?”
So…this makes no sense. If I had to guess, I’d imagine your girlfriend exhibits this kind of strange obsessive behavior inconsistently, has occasional bouts of depression, and is no older than 30. Regardless of whether I’m right (but especially if I am), you should consider whether your girlfriend is suffering from something that requires a psych evaluation and get her one.
I think what it all comes down to is most people don’t really want rational debate, and don’t participate in debates in the hope of learning or even to help others learn. Most people participate in debates to feel superior/“own” the other side. The result is debates that are typically lazy, uninformative, and downright mean.
I think all of us have a little bit of this desire for superiority in us and we need to consciously make an effort to suppress it.