> If you are putting up code on GitHub to which you don’t have all the rights you’re actually in violation of their TOS and you are violating the rights of other copyright holders.

I can't find where in the TOS it says that you must "have all the rights [to the code]". It just says that you must not violate copyright nor other laws.[1] FOSS licenses by definition permit redistribution, so uploading to GitHub seems to be in-line with the license granted by the copyright holders.

What are the violations you mention?

> Contributors who add to existing GitHub projects are providing the same license to GitHub as the project maintainer though per the TOS.

Sure, but that's not the only way. If you contribute to a FOSS project elsewhere, those changes go under the same license of the project. Whoever you pass those changes to has liberty to redistribute per the terms of the license. The TOS is unneeded to legally redistribute FOSS-licensed projects with GitHub.

The TOS saying that you must grant GitHub these permissions is only to protect GitHub in cases where people upload projects without licenses.

[1] in addition to content restrictions, like no porn.