That's a really bizarre way at looking at roleplay and 3dx for that matter.
Firstly, most roleplayers like to do it with like minded people, well, its the only way you can RP on a realistic level, though I get what you mean when saying people playing the opposite sex, but the original questions are about roleplaying(not the 3dx pick-up game), which is playing out fixed or evolving stories and scenarios, and that sex doesn't matter in roleplay as the person is playing that role. The enjoyment comes from learning about that character and how your character meshes or reacts to them and the story.
The other part of your reply is most worrying, getting emotions and being hurt.. I'm trying to think of a way to say this without being too blunt, but I can't think of anything other than you really shouldn't be here for that.
Keep your feet planted and firmly keep hold of realistic expectations.
Well, not everyone plays 3dx for the same reason and thats good so.