GitHub has had a very positive effect for open source. For free software, it's a bit more complicated---the ease of collaboration comes at an expense that is not just antithetical, but actively works _against_ the goals of the free software movement. And here we now have a situation where one can assume by default (and usually be correct) that a given project is on GitHub, which is hostile toward software freedom while being host to more free software than any site/organization in the world.https://mikegerwitz.com/about/githubbub
Until recently, they made virtually no mention of software licensing; the consequence is that huge numbers of projects on GitHub are proprietary because they carry no license at all. I don't know if they emphasize choosing a license now or not. I know some changes have been made.
I have nothing against the _idea_ of GitHub---GitLab is a suitable replacement there. There are just changes that need to be made, and changes we in the free software community _want_ them to make. I and many others, including rms, have reached out to them. We need broader community interest and pressure. Avoiding GitHub unfortunately isn't a practical option.