I'd say that the core of your point is legally correct, but you are ethically arguing over what is, at best, a grey area. I mean, if the author is explicitly (by you) "allowed to be an ego maniac", then why isn't the user you are replying to allowed to judge them for it? The options available here are not merely to use it or to fork it: people being afforded the same freedoms you believe this maintainer should have also have the option to call them out over the result, no?
I'm not here to argue the morality of it. I'm just saying it's silly to complain about something and demand something of him. I mean I can demand a super model will give me a date but that doesn't mean I'm entitled to it or that it's going to happen. It's pretty much pointless.
The difference between this guy and the maintainer is that the maintainer did this guy a huge favor by writing this software for the guy where as this guy did nothing except complain about the free meal he's getting.
