Barton, I'd have to agree with you that there are both elements. I think there has to be something innate about our desire. I've tried the role of switch, and it does absolutely nothing for me. I get no erotic feelings tying someone else up (unless, I look at them and imagine myself in their place).
I'm pretty sure that I couldn't "learn" to be aroused by those actions... even though I know that I've been aroused by the thought of restraint for my entire remembered life.

I think the learned part is where we figure out, through trial and error, exactly what turns us on the most. IE: if you have an interest in pain, then you will have to go through the process of finding out just how much you will realistically enjoy. (for me, that limit seems to be moving higher and higher all the time)

My sig. oth. also tried switching roles (I guess that is obvious), and found the
experience of being helpless completely un-stimulating. I truly believe we are wired one way or the other, and a few are both... just like those who are born ambidextrous.