There are technical solutions to this. The old one was called hashcash, which a predecessor to cryptocurrency.
To get an account you would have to do something like $5 in electricity worth of computation one time, which you can do without giving anyone your name. But then if you do something foolish and get banned, it'll cost you another $5 (or however much is necessary to provide a sufficient deterrent) to get a new account.
Obviously now you could just have them pay (or mine for you) a small amount of cryptocurrency, which would then go to offset the cost of banning the spammers who still try their luck.