Justified? Hell, screaming at Batman and Robin was mandatory if you wanted to keep your fanluv credentials.
My only movie-related public outburst (well, other than the D&D movie, but then I was travelling with a pack, and we just MST3K'd that sucker right in the theater) was not actually during the movie.
You all see Mulan? Great film. Did a wonderful job of breaking Disney's 'dependent female syndrome'. Sure, she ends up getting married--but only after kicking ass and taking names, and pretty much deciding this is a guy she wants, instead of being a hothouse flower that settles for the first Prince Charming to come along.
I was positively delighted when I saw Mulan. Even the Disney elements (such as Eddie Murphy as Mushu) didn't bug me too much.
Then the then-gf and I swung through the Disney Store as we walked through the mall.
And on shelf after shelf, there was exactly one toy--Bridal Mulan. Yeah. She was in that freakin' powder-and-rouge for maybe ten minutes of screen time, and even that was roundly mocked as archaic and insulting... and that's what little girls were being told they should aspire to.
Meanwhile, the plastic sword? That had the Prince's name on it.
It took fifteen minutes for the then-gf to drag me from the store, still shouting condemnations at Disney's product division.