I get what your saying but I think it’s not the best way to describe it - “GPL is property”? Hardly - it’s a societal common good that can be used by anyone interested in helping that common good.

Are parks “proprietary”? I can’t run my car dealership from one, so it’s …proprietary? No. So using the terminology of “proprietary” doesn’t do justice to what it actually is.

The phrasing is a little awkward but I like the sentiment: gpl software is owned by the public/humanity/the commons/etc in the same way something like the grand canyon should be.