[] Agree to the mission. Steal a few dozen cows, sow chaos, escape.
[] Argue that they should send an armed delegation to confront the tribe. If it goes in with shinobi support, then surely they'll get the message?
[] Argue that they should ignore it. Or rather… keep the young men as hostages and continue on as if nothing happened. If someone comes to ask for the young men back, then… and if they don't, that's a dozen less people the other tribe has to try the same thing again.
I guess that by confront you don't mean to attack but to ask them what the hell is going on, right?
The tribe we are protecting is already scraping by, so I don't want to eat up resources on them like that. Considering how they refused to back down, I guess they are either a)desperate (so something really bad happened to them) or b) they were coerced into doing it. It could also be retribution for something our tribe did (read, the secret mission that the suposed-ninja-family did, but then they wouldn't be so quiet about it. So I'm betting coerced. If that's the case, I doubt we can convince the prisioners to talk (specially since we don't speak their language), but sending people increases the chances of finding out what is going on. Besides, there's this quote of the update:
"So, no harm done," Masato said. "We let them off with a warning? Don't do it again, young man, with your chakra and your near-shinobi level skills?" Masato asked it with a frown, as if he actually thought that's what should be done, but the way he framed it only left one answer.
The way it's phrased it sounds like Masato is guiding the conversation. Sure, he doesn't want to go in a rampage, but he still points out the problem of not acting, though subtletly. I bet that if we argued for ignoring the problem we would have his "support"... and would be more difficult because of it. he might have a secret agenda.
Finally, a comment to rise the paranoia
It began with a sound like a bird cawing, loud and long, and then from behind a rise in the hills they came.
It might be just me grasping at straws, but we alreadyhave faced someone with bird summons in this Act, haven't we?