I'm going to gossip and potentially alienate a friend
Why would you want to risk doing that?
Because I don't want to be seen with this person anymore, it ruins my reputation.
Putting your reputation above the feelings and emotions of others is just plain wrong. You shouldn't talk behind someone's back to begin with, but to knowing that you will potentially alienate someone doing it and going through with it makes it even more wrong. Relationships mean much more than reputation, and any reputation you get from talking badly about someone can't be good.
Okay.. I don't appreciate the lecture but I agree.
I'm sorry to lecture you like that.  I'm glad you agree now though, and I hope your relationships benefit from that advice in the future!