Well, that would require github making some changes server-side, but it seems like an entirely reasonable thing to do. You can browse the source, but you can't

Well, that would require github making some changes server-side, but it seems like an entirely reasonable thing to do. You can browse the source, but you can't really download it until you pay. There's no reason why free software should just be given away. The point is to make sure users have the source code and the permission to modify it and redistribute it. It was never to make sure they don't have to pay in order to acquire the software. Sure, if they can redistribute it, perhaps they could undercut you, but if we believe that piracy doesn't really hurt sales that badly, it seems likely that this secondary moneyless distribution might not substantially hurt the primary one.