Ok well, the modern web technology ecosystem is incredibly featureful and flexible, it allows a huge array of options for building rich interactive applications, all delivered to your browser on-demand in a few seconds.
Sure some of the technologies involved aren’t perfect (and I challenge you to find any system that feature-rich that doesn’t have a few dark corners), but there really no alternative option that comes close in terms of flexibility and maturity.
I mean. Sorta.
When you use some service you have some expectation that they’ll treat you fairly and predictably. Sure their Eula let’s them do whatever the fuck they want legally but that doesn’t change the fact that if they opt take certain actions (like arbitrary taking people’s usernames) then they risk losing user trust.
If the admin just took your username one day would you just quietly accept it? What if they edited or deleted your comments? Would you just shrug and say “well it’s their site they can do what they want” and just walk away?
Look what happened when Spez got caught editing posts on Reddit, for example. Massive user outcry.
Dude’s allowed to be annoyed about it.