Why do I always have to oppose people?

Everytime somebody says something I just have to oppose their point of view and come with an idea that counters theirs (even if I agree with them), and when they defend their position I end up pressing more until it becomes an argument. Even when somebody just says something positive, my first instinct is to point out the flaw.

Why do I do that? I realize that it's to my detriment, but could u speculate on what could be the root to this behaviour?