correcting someone else's child?

I grew up in the "it takes a village" family. I was corrected by parents, parents friends, and family. Never physically of course just verbal correction. My two best friends have children. When we spend time together and their child is out of hand I do verbally correct the child. One woman I've known since we were nine and she never gets upset when I correct her son, the other I've known for a few years. For example last night my friends daughter was poking and smacking a stray cat in the face as she sat on her mothers lap. While her mother just watched  and said nice kitty. After the fourth smack I sternly and calmly without yelling said "AJ, we don't hurt kitty's, we have to be nice." She looked at me and did it again. Again I looked at this little girl " if we can't be nice the kitty will have to go home ." She stopped and played nice. SO says I shouldn't correct other children. I told him if my daughter does that some day and no one says a thing to her, I'd be very mad with every one for not telling her no. That's not acceptable behavior. I believe that everyone should be setting a good example for the child parent or not. If my close friends don't say something to my miss behaving child then how can I trust them to watch her?