What we can sing, and where, has been somewhat limited ever since the first copyright protection laws were written in each country. Before that, in the U.S. at least, people simply stole other people's published songs, and re-published them shamelessly, profiting from the theft. A common thing was to write slightly different words to a popular tune, and publish them under the original name, for example the copycat versions of Tenting Tonight and Man on the Flying Trapeze that I have seen.

The copyright laws helped change that. Probably a good thing, especially for people who actually write/wrote songs for a living, like, say, Irving Berlin.

Everything is a compromise. Every time you right a wrong, you are in danger of committing another one because no law can take in every case ahead of time.

Any song, copyrighted or not, can be sung for personal pleasure in the privacy of one's own or one's friends homes, where no money is being exchanged or received in connection with the occasion. My own family used to gather around the piano and sing dozens of copyrighted songs -- that's why they publish sheet music.

Making a profit from singing copyrighted songs is quite different. Yes, people are limited in many ways in deciding what they will do to make a profit.

There are plenty of uncopyrighted, public domain songs for folk singers to sing for money, or in venues that charge money, or in public venues of any type. And, as several people have pointed out, lots of folkie song writers freely allow their songs to be sung by others.

If you want to perform copyrighted songs, well, you may have a problem. But there's no one who has the right to do everything they feel like doing! So, there are restrictions on singing most copyrighted songs for other than personal pleasure. That occasionally limits our doing what we feel like doing. Pick another song and keep on singing.