For me sometimes its not the act but what it could feel to me. I have a dick and therefore if I read a dick being sucked etc then I can feel what the character feels. I don't see anything wrong in that.
I have watched gay porn yes but as a visual it just didn't really get me horny or hard.
However, reading stories of guys playing with one another in casual or serendipidous circumstances is a topic of erotica that really gets me going most.
For me I think it is because I do get excited by some cocks but actual guys just have never had an effect on me.