Bashing tavern drunks gives +/- points to town instead of barkeep relationship.
Unless I missed something, something that altering a barkeep's perception of you can bring (such as paying less to treat your troops), I think it's only natural to make the switch. If you prefer RP over practical reasoning, news travels fast in small communities, and everyone goes to the the tavern sooner or later. That bum was stepping on toes long before you arrived.
While I'm at it, it would be nice to apply the same to the first quest you are offered, for the Merchant of {townname}.
Considering that a) the quest has been shortened and that he's no longer an undesirable, as was the case in Native, b) what you do for him, and c) that he, being an influential merchant, is constantly in touch with the townsfolk, him singing praises about you to others sounds about right. Insignificant as it may be in the long run, that quest would mean much more if you scored points with the town (instead of some random guy you'll never see again) when starting from scratch.