[xyzzy_plugh]

I'm confused. Copyleft doesn't grant a right to contribute upstream. It's perfectly reasonable for a maintainer of a copyleft project to say "I only accept contributions if you give me $1,000."

Copyleft grants you the right to make changes and redistribute the resulting work under a compatible license. If you have a problem with CLAs, don't sign them. Many people do not care.

Even without a CLA the author could simply remove contributions and still relicense. This isn't novel, and has been done before.

Obviously it may be difficult to remove contributions.

[josephcsible]

It's rare for an important software project to be 100% a one-man show. Combined with the difficulty of removing contributions, wouldn't rejecting CLAs basically keep this kind of thing from happening at all?

[xyzzy_plugh]

At what cost? The livelihood of the maintainer? Nah.