Well some people (not me) believe that if you are a Dom you are a Dom and if you are a Sub you are a Sub.

I think it just comes down to the idea that, if someone "submits" to someone and gives up control then they must be in that "mindset" and I *guess* people feel if that is the case then they can't get into the "Dominant" mindset.

^-Ramblings by me and reflect my view on the above