This is something I have tons of experience with (mostly on the dom side), but you would not know that to meet me.  You can still be a complete gentleman, a loving, tender person who cherishes women on every level...  and still have a dominant or sadistic streak that plays out ONLY when you are with someone with whom submission, or masochism, is a heartfelt desire.

The problem, and this is a huge problem, is that people take the shortcut.  BDSM is not at all as simple as tying someone up, or surprising her with nipple clamps or a flogger.  It is a dance, a conversation, that takes a long time to develop.  No matter which person (gender) is the D (dominant) party or the S (submissive) party, there is actually some magic playing out that gets down into our most primal, base feelings about masculinity, femininity, strength, vulnerability, and for most it ties deeply into emotions that go all the way back to early childhood.  I cannot tell you how many submissive women I have talked to over the years who say something similar to "I remember watching Bullwinkle and when Snidely would tie Nell to the railroad tracks, I could actually physically feel my desire to be her down in the pit of my stomach, it was visceral...  and I was 8 at the time."

If you race into it, it will end up feeling shallow, hollow, a role play, and nothing more, so nothing really honest and revealing gets discovered.  But when you do it right...  The D starts to develop a deep trust that they can express their inner caveman/cavewoman, they can reveal "taboo" desires and fantasies, without any fear of judgment or disapproval.  Even if what they desire may be well beyond the comfort zone of the S to actually try, there is still deliciousness in being accepted, and the other person saying "I don't know if I can do that for you, but it is moving for me that you shared it with me and trusted me with it.  Likewise, a trust develops in the heart of the S as well, this deep confidence that submitting to you doesn't diminish me, doesn't make you see me as less, or weak, or lower than you.  And if there are any elements of pain play involved at all, that same things apply...  The inflictor doesn't have to fear that "why would you want to do this to me, what is wrong with you?"  And the masochist doesn't have to fear the "why would you be willing to allow this, what is wrong with you?"

Most people are actually a little more towards the judgmental end of the spectrum.  Most people tend toward "If it is not something I want to hear, I'd rather you keep it to yourself."  If you are more of a cut-and-dried kind of person, then it's probably not for you, hence the term "50 shades of grey".  The almost mind-boggling intimacy of it cannot be found on the surface, by people who take things at face value.  You have to dig and your heart has to be filled with forgiveness and acceptance of whatever it is you uncover, in the other or in yourself.

But if you go into it with an open mind, longing for understanding, acceptance, wonder, curiosity...  A yearning to give acceptance to another...  It can be unbelievably intimate, and thus, for some people, almost gut-wrenchingly erotic, a different kind of eros than you can experience any other way.

But, what do I know, I may very well be all wrong.  :p

I have to say though, I don't really look for this in the hobby, as those here that I have met can attest.  It takes a level of communication and sharing that takes a long time to develop over many conversations, and that's hard to sustain in the confines of the hobby.