*shrug shrug shrug* Again, I'm not saying you don't have a point. I'm just saying I can't blame GM's for having their reasons. Maybe they just find humanoid characters easier for them to manage. I don't know, I'm not them.
Also, hate to play devil's advocate, but it's also a bit close-minded to assume that every GM that only allows humanoid-looking aliens is doing it for sexual reasons, methinks.
Like I said, you could've tried debating it with the GM who rejected you in the first place. Then, one of three things would've most likely happened: 1) You learn that the GM is too inflexible to handle any questioning and you're better off without them. 2) You manage to convince the GM that the alien race you'd suggested is perfectly doable and that they have no reason to not accept it. 3) If the GM is able to effectively argue against you, then you gain a better understanding of their argument because maybe they have a good reason for placing such a limitation.
Or maybe they don't have a good reason. I don't know. I wasn't there, and I didn't ask. *shrugging continues*
If you think it doesn't make sense for an RP like that to not accept a wider variety of aliens, then that's fine -- go ahead and start your own RP (or have Ceph start one or something I dunno). I think it's a great idea, really. And, if sci-fi RP's that do accept more diverse aliens really are as rare as you say they are, then I'm sure you'll attract plenty of players who share similar frustrations to yours. I'm not trying to say you don't have a valid complaint or anything. For the most part, you raise a good point. I just can't say I agree that all these GM's are really in the wrong, since I don't know much about their stances on it or why they placed such a restriction. Maybe, the way their RP's are structured, their way makes a lot more sense. And, given the fact that I, personally, tend to value structure/activity flow in an RP far more than the actual content/concept (at least from a GMing perspective), I can't fault a GM for placing such restrictions if it makes it easier for them to run. :/
But, seriously, go ahead and start an RP with Ceph if you think it's a good idea. (And I'm not trying to say that in a sarcastic or passive-aggressive way; I do sincerely think you should go for it if you feel so strongly about this.) I'm not trying to say you're wrong or anything so I apologize for whatever emotional state this is putting you in. :/