I had someone tell me they don't watch DC movies because they like Marvel.

As do. I don't understand stand people with the either/or mentality.

I feel sad for people who limit themselves that way

I can choose between them, but I can't have one without the other. I think Marvel has better heroes, but DC undoubtedly had better villains.

Each has its merits which is why I enjoy both. But you make a very good point :)

When someone is heavily biased against DC i always wonder if they had a traumatic experience while watching a batman movie or if they are just this bigoted about everything

I say the latter