Agree, OP, succinctly put. IMHO if one finds it "weird" to have a certain type of race with both genders playable, it is probably due to gender stereotypes, homophobia of some sort, and/or sexism.
With Viera as an example: bunny ears are often associated with beautiful, enticing young women that are unashamedly sexually appealing. If one finds that untroubling, but replacing "women" with "men" in that description makes it offensive or "weird", I believe there is a problem. Similarly, making a big, weird looking lizard race male-only sends a negative message that visible, obvious physical strength and being unattractive is only acceptable for males.
Sorry for the mini rant, it is a pet peeve of mine when only female characters are sexy-fied while only male characters are big and unattractive because of such (not) wonderful reasons as: "eww, who wants to look at that" or "dude, that would be so gay". Single gender races are often just an extreme manifestation of this attitude.