Standing up for someone once in front of everyone can mean more than being nice to them in private for months.

Private kindness is real and it is also deniable, which is why it does not change somebody’s position in a group. Saying something out loud, once, in front of everyone, alters how the rest of the room treats that person from then on. The risk you take in that moment is the whole value of it.

If somebody is being treated badly in front of you, say the plain thing at the time rather than apologizing to them afterward. It does not need to be clever or long. One sentence in public does work that months of private sympathy cannot.