I dunno what else to say on the subject of gender roles than what I've described about me. Gender is basically the outward appearance you choose to show society. We are designed as binary creatures physically and it's only natural to have 2 rather different "genders" and for a lot of people it's a lot easier to drift towards one "norm" than to blaze their own.
That's definitely the case for me. How I sum things up is I'd rather be a tomboyish girl than a girly boy, as I feel I can shift my identity over a little to match an acceptable "girl" than say stick out as a strange guy. I actually applaud people like Nobu who have the tenacity and self-confidence to be able to say "you know what, I conform to neither, and wish to be just me" and are able to live on the sliding scale of gender identity rather than fit into the notches like most people.
If I didn't have such a strong and vehement hatred of being a "manly man" and had the courage to just be me and ignore society's judgment, I'd probably just be a really girly gay guy. I don't outright hate having a penis, it's... a detatched indifference, kind of like an appendix. Something that doesn't really bother me but serves no purpose physically. Honestly what I get between my legs I would actually most likely leave up to my partner as really it's for their enjoyment =P
As for BDSM... well I'm terrified of bondage and I'm definitely not the domineering type but Trance has definitely enlightened me to it as more of a way for couples to express total trust and faith in eachother in ways just jamming it in don't do. And it has little to do with pain either, as I hate inflicting pain on others nor would I want pain inflicted on me. Pain and bondage may be the most graphic and well, most "unique", way to practice it, it's hardly the only way. If anything the way BDSM works for me and Trance is I would crossdress him and doll him up and make him do my biddings in that manner :3
It's less about what you use and what you do, and more how you approach your relationship. And honestly BDSM just gets singled out because it seems so extreme compared to "normal" couple interaction, but if anything it's nothing different, same roles and same objective, just different toys used =P