@colinsmatt11 I'm becoming convinced that the overstepping of what copyright and contract law allows by BSD licenses and MIT expat would make such licenses nonfree, if complying with the license terms wasn't trivial.

The odd one out it the BSD-4 clause, which can possibly become nonfree just with standard free software development practices, as complying with the license becomes difficult or impossible if there's more than one copyright holder:
"3. All advertising materials mentioning features or use of this software must display the following acknowledgement: This product includes software developed by the <copyright holder>."

Although it's probably the case that neither copyright nor contract law permits such agreement from being enforced - it's not good that you need to agree to a potentially nonfree term even if it's technically unenforceable.


While I'm not a supporter of traditional advertising, but it could be argued that a manual on the usage of some software counts as an "advertising material".

For a worst case scenario, lets say you want to publish a physical copy of a manual on how to use some software with say 30 pages - but there's 1000 copyright holders - clearly having to write 100 pages of: "This product includes software developed by the <copyright holder>" will make having the book printed infeasible, as not many people are going to want to pay however much a book of 130 pages costs, when the book only has 30 pages of information.