I think this whole "debate" is too vague. It's too difficult to "judge" some vague "warning"
the real life example for work situation could easily go the other way.
Let's say Neighbor #1 warned new neighbor #2 that neighbor #3 was a convicted child molester. If this was in fact true was neighbor #1 just a horrible busy body or in fact someone with a geninue concern for the new neighbor? But if neighbor #3 was completely innocent and #1 knew that, the #1 would certainly be spreading malicious gossip and that would be wrong. What if #3 was wrongfully convicted of a crime in the past, and #1 knew THAT fact but had no way of knowing it was an incorrect conviction?????
I think there just isn't enough information to "judge" the person giving the warning as the "bad guy" here.
Personally, I haven't received nor given any "warnings" here but if someone with a good heart was generally concerned and felt I should be aware of something I for one would appreciate the heads up and try to be a bit more aware and make my own decision.