I think school scan reasonably ban certain speech on school grounds and/or during school functions for purposes of instruction and decorum.
Part of a schools job is teaching young people about appropriateness, tact, politeness, etc. Something can be both true and impolite, tactless, and inappropriate, and it’s reasonable to have rules about those things and punish those who ignore them.
I do think schools tend to overstep their grounds on this, and try to regulate student behavior at all times, which is not reasonable. Outside of school, that’s a parent’s job.
I don’t think the government should be able to ban true speech (and probably shouldn’t be able to ban most not-true speech either).
To answer the OP: when your starship has come upon a powerful but paranoid and xenophobic alien race that wants to avoid all contact with outsiders, and their memory-wipe technology doesn’t work on your crew’s android, so you order him to actively suppress any and all information about these aliens before the memory-wipe takes place.
I know this is a bumped zombie, but it’s super relevant. Today, I had a sit-down with two students. One student is overweight. The second student called her fat. I–a government representative, a public school employee–told the second student to knock it off.
I do this all the time. “Oooh, Sarah farted!” Knock it off. “You daddy so poor you don’t EVEN have new shoes!” Zip it. “Mr. Dorkness, there’s a spider on the window!” Kid, we’re in the middle of a freakin’ lesson about nouns, shut your mouth and look at the board!
Schools censor speech all the time, in order to facilitate the learning environment. I’m a big fan of having that power and can’t imagine being able to do my job without it.