A rumor travels lightly because the people carrying it leave the consequences behind.

Passing something on is cheap precisely because the cost arrives somewhere you are not. It takes a second to repeat, and the damage happens to a person who is not in the room, over weeks, in ways nobody traces back. The lightness is not incidental to how rumours work. It is the mechanism, and it is why obviously decent people take part.

Before repeating something about a person, ask whether you would say it in front of them. If the answer is no, that is enough information. Letting a story stop at you costs nothing and is invisible, which is why it so rarely happens.