I can respect that... however, sometimes it's not worth fighting... you can export your bugs, content, etc from github, and import into self-hosted gitlab, or other options if so desired. Then you lose the community aspect, but it's not exactly hindered.
I just don't see GH turning into SourceForge. I know it can happen, doesn't mean it will, and if they (GH) ever head down that path, people will exodus.
GitHub is far more intrusive than SourceForge (don't get me wrong on quality though... SF is a piece of crap). Remember GitHub has a lot of people's credit cards! Even Facebook doesn't have that.
GitHub could easily some day sell user information (if they are not already). The could sell it to recruiting companies (like my own company) or they could sell it even to ecommerce companies like Amazon.
Comparing GH to SF is not really even remotely useful because things have changed so much (in terms of technology, biz models, users ...etc ).
I just don't see GH turning into SourceForge. I know it can happen, doesn't mean it will, and if they (GH) ever head down that path, people will exodus.