if someone steals from your follower, be it a person, merc, slave or brahmin or whatever, it should count as someone trying to steal from you yourself, and you can retaliate with violence.
I'm getting sick of mining with my brahmin to carry the ores, then because it's following is a little messed up (he sometimes just gives up and stands still, the lazy bugger. He's not over his carry weight, either) he stands a few feet away or out of sight, someone steals the ores from him because he can't do shit about it, and I can't punish the little sod who's too crap to even mine his own stuff.