It's a fetish, and one I consider unhealthy.
Elsewhere men and women don't stand for being dominated, especially in the things they love. They want to flourish.
So with something as intimate as sex, WHY THE HELL would they willingly deprive themselves of any chance to be truly loved, and instead have the other side dominate them like they were some sort of slave?
Perhaps it's a game of let's pretend, but it's really blurring the lines. A portion of people who ask to be dominated, their tendencies could reflect in the way they behave. Be subservient in one thing, be subservient in other things. I suppose that isn't true with other people, but... I cannot stand that sort of subservience in any way, shape or form. Especially when that same subservience has been a massive depression trigger in people I know, who once loved to be dominated. Some have suffered that to the extreme (read: rape).