[ramshorns]

Of course; those are freedoms 0 and 1 guaranteed by the license. It seems like "use" sometimes means "include in a downstream software package and redistribute modified versions of".

[fluoridation]

My point is that just having the GPL doesn't guarantee that modifications will be contributed back or published, even without violating the license.

[pabs3]

Right, GPL only requires contributing forward, to the downstream users. It is only through creating a culture of working upstream and or reaching out to downstream redistributors that a project gets any contributions back, including financial contributions.