We should have male space marines. Why should it be an all-female institution? Even if we buy into the WG excuse that the empress needed complete XX chromosomes to make the primarchs, she is still the goddamn empress. Males make just as much sense as female space marines, they would be all so pumped up in hormones to matter.
As for the "they are supposed to take inspiration on nuns and sororities, which did not allow males and called each other sisters", I think we crossed that line when they became super-armored darkgrim futuristic space nuns.
And fulgrim did nothing wrong.