Of course it's not weird. It's empathy. Plenty of straight people get offended by the word faggot and lots of white people wont accept people using racial slurs. It means you're a good person.
I don't think you must be a member of a certain discriminated group to emphasize; I'm not a woman, but hearing of sexism within the LGBT communities, and how people will deny, deflect, and defend against sexist issues brought up makes my blood boil. I think most people don't give too much thought to what happens to the 'others'. It's easy to forget just how many different types of people, and how many different communities are out there, with have their own sets of issues. So, keep up the good work; you're bucking the trend, fighting stereotypes and injustice at the same time. Also, the fact that you identified as bisexual for a while and might have witnessed biphobia first-hand could have also made you more aware of issues other gay men might be uninterested in or unaware of.
Exactly! I think it does have a lot to with that. I guess I'm so against biphobia, because I didn't like it when I thought I was bisexual. So why would I be unfair to real bisexuals?