If the situation were renting out a stand-alone apartment or house, I agree entirely. Gender discrimination is unwarranted.

In situations where you're renting a bed or a room in a shared common space — I don't think it's unreasonable to be more selective about gender. Is it discriminatory for colleges to not group men/women together in dorm room?

Again, look at the severity disparity here:

would it be socially acceptable for a woman to say "I don't want a male roommate?"

would it be socially acceptable for a white person to say "I don't want a black roommate?"