Twitter is a private company and is not a monopoly, but anticompetitive behavior should be called out, the same way that (many) of us did about Instagram blocking links to competitors and Facebook pursuing anticompetitive policies against services like Snapchat. There are plenty of people who have campaigned for iOS to allow 3rd-party app stores that are calling out Twitter's current behavior. There's no values dissonance there, Musk banning the original account/journalists is 1st Amendment protected activity, blanket-banning Mastodon links is (
potentially, but I don't know how likely it would be to ever see a court battle) anti-competitive.
More to the point, outside of antitrust there are plenty of people that have specified in the past that Twitter is a private company and can do what it wants, but that its moderation decisions are subject to private scrutiny and that consumers can complain about them. And importantly, that doesn't mean that all of its moderation decisions are universally good or bad.
"People are allowed to complain about private moderation decisions" != "All moderation decisions are exactly the same and if you complain about any of them you have to complain about all of them"
It's OK to point out that reporting about someone else posting flightplan data is different from subtly encouraging people to bomb hospitals. The point of Twitter being a private company is that it's not the government and it doesn't have to be blind to those distinctions. Private speech/moderation is the place in free speech debates where we are allowed to make actual value judgements that are more nuanced than "all censorship good/bad".
It's also completely valid for people to point out that Musk hasn't banned doxing, he's banned an extremely narrow category of doxing that is specifically designed to get rid of the one account he doesn't like, while still allowing accounts like Libsoftiktok to stick around. It's completely valid to point out that Musk announced this policy at the same time that he posted a public license plate on Twitter and asked his followers if any of them recognized it. It's valid to look at that behavior and think, "huh, maybe this has never actually been about free speech for him."
But yeah, it's not illegal for Musk to ban journalists. It's a bad business move and it's going to prompt more people to jump ship off of Twitter and it's going to prompt more publishers to think about how they disseminate content and how much they should use Twitter as part of that strategy, but it's not illegal. Anticompetitive behavior might be different (although no lawmakers cared when Facebook did it, so I'm not sure any of them are going to care now).