Plenty of software freedom advocates do believe that copyright is evil and copyleft is essentially using copyright against itself as a temporary stopgap until copyright can be abolished completely.
What I don't get is why it is considered more ethical to provide more benefits to the users? Wouldn't Public Domain then be the most ethical license of all?
One could argue that society as a whole would be better off if zero marginal cost things like software or poetry, or information in general, would be freely available to everyone [1]. But that raises the question how such public goods ought to be financed. In today's capitalistic society it doesn't seem like a very serious proposition. In today's world, the choice is often not between proprietary software for solving problem X vs. free software for solving problem X, but between proprietary software for solving X and no software that solves X. And I don't think society as a whole is better off by not solving problem X unless we have a FOSS solution.
[1] Even that has limits. We probably don't want detailed instructions for making, say, biological warfare agents publicly available.
Only by uniting and making laws, including contract-law, can the weaker actors, the majority, guarantee a fair and better society for everybody.
I do like the GNU copyleft licenses I think that is a great idea. But then to say that because I released my software under copyleft everybody else must do the same, or I call them unethical, sounds self-serving.
I don't believe that society would be better if "zero marginal cost things like software or poetry, or information in general, would be freely available". Is there any evidence of that?
Human nature is that people will produce what benefits them --and others-- the most,. Therefore they choose to grow crops that give them the biggest profits. Think about pharmaceuticals who invest billions in research for new medicines only because patent-laws exist. That does not mean we should give them unlimited power to exploit their patents. We can make a law that progressively taxes exploitative pricing, however that is defined.
contributing back would mean whatever change you put in your fork must reflect in upstream which is not something all upstream users would accept always but its not a requirement.