Github's corporate culture appears to be very anti-woman. There is plenty of available evidence to this effect. There is very little apparent diversity (of any sort) in their large team. https://github.com/about/team
Using Github contributes to the success of this monoculture and encourages tech leaders to revere and duplicate this model. It makes tech more difficult for people outside of that group - the white, straight, male group. It makes tech culture worse.
If I'm aware that you host on Github, I will make sure to consider what your competitors are doing before I use your service.