I don't quite "get" subordinate, so maybe we choose that...but submissive/slave...do we choose that anymore than we choose to be heterosexual/homosexual? And where do switches fit in?
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You bring up a great question of essentialism (W/e are what W/e are because W/e are... sumus ergo sumus) and constructivism (W/e are what we desire to become).

Are you submissive because you are by nature, or by choice? Am I Dominant because that is who I am or because that is how I have constructed myself through my experiences?

In the nature v. nurture debate, which is really what this is, both extremes are naive, in My view. But the middle of the fence is naive and fallicious, too. No one comes into the world desiring the aspects of the lifestyle, but they do scratch that itch inside of U/s that evades description.