I think there are lots of great comments, and a great topic, here's some of my thoughts/feelings.
Personally, i subscribe to the “spectrum theory” of human sexuality, and wow, it can be varied and complex, eh?
i think the myriad labels and terms we come up with like “Dom, Top, bottom, sub, versatile, straight, gay, bi, trans, ad infinitum,” can either serve us or we can serve them. Many object to “labels," not wanting to be defined or boxed by them. i do not believe labels ever define or box us, rather some will use them to define or box and end up trying to fit the person into the label. On the other hand, labels and terms are part of what we use to communicate and connect. We'd be kinda handicapped without words, terms, labels. i do not think there is anything intrinsically wrong with them, but how we use them, whether they serve us, or we serve them.
Where i am going with this is i think we spend a lot of time hiding from reality of who and how we feel because of the social reputation and baggage that comes with those who are serving labels. E.g., a guy grows up and lives primarily in say a conservative religious culture that has a negative take on male with male sex, calling it “perverse, sick, sin, etc..” So, even though his reality is he likes to have his cock sucked by other men, it violates his cultural conditioning.
i think we often are conflicted by the reality of who and how we are with the cultural notions of who and how we ‘should’ be. We spend a lot of time rationalizing to make ourselves fit our own particular cultures accepted ‘norm’ because we do not want to be rejected. At the same time, we are not really experiencing full acceptance of who we are, so some end up on the DL, getting their cock sucked in order to experience affirmation and acceptance of that part of their self.
i also believe, thrown in to the whole “spectrum” thing is the factor that some are Tops. i've been with a lot of guys who either bred me or i sucked, and they were in a relationship with a woman. i think with a lot of these guys, it's not a question so much of being straight, bi or gay, but they are Total Tops and are not wired to ‘reciprocate.’ As a total bottom, that suits me perfectly, we are sexually symbiotic. :-)