Earlier quoted context omitted.
Copyleft is not required, free software is a gift freely given. Even public domain is ok (weird places like Germany that don’t have public domain notwithstanding). What must be rejected is nonfree licenses like the BSL.
BSL is preferrable to completely closed because at least researchers can look at it now and it will eventually transition to open source. If Windows XP was BSL licensed then Wine would have a lot less trouble now.
A BSL project could say, hey, look at this guy stealing our code!, even if I’ve never seen it. I could have, and that opens a plausible risk I wish I didn’t have.