You wouldn't want goblin visitors to apply goblin ethics on murder, for instance
Funny you should say that. I decided my tavern is too full of visitors. My locals can't even get in. I happened to have a goblin in the fortress, so I appointed him tavern keeper, with the hopes of murdering all the visitors. Unfortunately, there are so many that he can't seem to serve them fast enough. I tried to give him helpers, but my whole fortress is full of hardened military dwarfs and they just go to personal combat training instead. Sigh...
What you say sounds backwards. If you wanted to get rid of the visitors it would seem good to me to only have the visitors in the tavern, rather than the locals. It should be easy to target the locals specifically, though, by setting up a citizen only tavern with a close by booze stockpile, lots of tavern keepers, and removal of the training facilities from the off duty military.
I tried to make a visitors only tavern by placing it out of the way and have a resident only tavern centrally, but for some stupid reasons the locals insisted in running back and forth to the visitor tavern all of the time rather than use the good local facilities. (I wasn't trying to set up a visitite mine at that time [although it would prepare for one], but rather set up a vampire visitor trap, but it didn't work because I found all visitors, including petitioners, always go to the target zone first, and then from there to petition, so the trap would get every petitioner. I'm working on a new, better design...).
@Thisfox: It's unlikely visitor killing would induce war with your trading partners. It seems to take a lot to push them into war.
If you don't want visitors, just lower the visitor cap in the appropriate .ini file. Most of those you have will drift off, and the remaining ones will be the bugged overstayers.