There was a situation the other day, where an acquaintance of mine was going to eat a bagel that he very much liked. Unknown to him, was that the bagel's ingredients contained gelatin. I looked it up to make sure and then I notified him.
I remember, once in the past, in similar situation, someone once told me something along the lines of "I shouldn't have told him because it won't be sin for him to eat the haraam since he didn't know, and that is was very unobvious."
Did I do the right thing, or how correct was that particular someone from the past?