Being a bad influence is easy. It takes zero effort to make people worse.

Pulling people down requires nothing. Go along with the meanest joke, agree that the effort is pointless, be first to say nobody cares, and the whole group slides a little. Lifting takes attention and it works slower. That gap in effort is why the downward version is so common and so rarely noticed as a choice.

Watch what you add to a group this week rather than what you take from it. When the conversation starts sliding, you do not have to lecture anybody. One sincere thing, or simply not laughing, is usually enough to stop the drift.