I don't really think anyone is 100% straight or gay, so I couldn't possibly put myself at 100% straight. I do have some interest in seeing other dicks, but its more about comparison for me, and my real attraction to this site was having a place to anonymously show off and get attention for myself.
Other than some mild experimentation when I was young I haven't engaged in any sexual activity with other men, and I don't want to. However, I do recognize that there are some things that can turn me on when watching porn that wouldn't turn me on if they were happening in reality. For example, someone being exposed or doing something sexual in public whether male or female, guys who appear to be pushing their boundaries and doing something sexual, transexual porn. I don't think I'd be into any of these things if they actually happened, but the concept when I'm viewing from a safe distance is arousing.
Another factor is that you'll just get more attention and more feedback on your pics and vids if you are some percent gay on this site. I stand by my 1%, but I would have been less likely to enter that value if I didn't think I would get some benefit from it.
Finally, I don't like porn when a man and woman are having sex and the guy has a repulsive body and a small penis. This must mean that I have some preference in the appearance of men in porn. I think if one were truly 100% straight they would have no preference in this regard at all. The man could weight 700 lbs and have a penis that isn't visible under his fat and it wouldn't matter. I don't think anyone actually feels that way, and that's why I doubt anyone who claims to be 100% straight.
Now that I've answered this, there are several other threads in this section of the forum asking the exact same question.