Free software licences can be roughly grouped into permissive and copyleft ones. Examples are the BSD and MIT licences for permissive and the GNU GPL for copyleft. A common argument is about which one is more free.

Permissive licences typically allow using a different licence for any derived works. In other words, if you release some software under a permissive licence, I can make changes to it and release the result under almost any other licence, including a proprietary, non-free one.

A copyleft licence requires a derived work to be released under the same licence as the original. I can't make my own version and make it not be free (unless I get all copyright holders to agree to a licence change).

This is the crux of the dispute of relative freeness. A permissive licence lets you do things that a copyleft one forbids, so clearly the permissive licence is more free. A copyleft licence means software using it won't ever become non-free against the wills of the copyright holders, so clearly a copyleft licence is more free than a permissive one.

Both sides are both right and wrong, of course, which is why this argument will continue forever. Because there's no clear objective winner, the arguments easily get very, very hot.

A related argument which type of license is better for doing business with. Many in favour of permissive licences claim that it's better for business, because you can do things in more traditional ways: sell non-free licences to customers, for example.

However, making a living or running a business using a copyleft licence is certainly possible, and not even unusual. It may require coming up with a different business model. In fact, because almost all software development is really a service business anyway, it doesn't necessarily matter a whole lot what the licence is, as long as your customers are happy to pay you for support and feature development.

A word of warning. Any discussions about these topics should be treated carefully. It's like using nitroglycerin: it's an important compound with several practical, industrial uses, but do not, repeat, DO NOT make juggling balls filled with it. If a discussion about the relative freedom of licence types becomes heated, step away. It's not worth participating anymore. The best case scenario is that several people get their feelings hurt and stop talking to each other, possibly forever.

If you want to make a choice between permissive and copyleft, you need to do it based on something else than their relative freeness. You might prefer permissive because it makes it easier to combine with other licences. You might choose copyleft because you don't want your software to ever become non-free. Or you might choose based on the most common licence type in the community you participate in. Or based on the length of the licence, or which one has a prettier SHA1 of the contents of the licence. And if anyone questions your choice, avoid getting into a fight.

Disclaimer: This was written by someone who has chosen copyleft and has earned much of their adult salary writing copyleft software.