Archer in this one just blew me away... "What gives you the right to take prisoners?" Yeah they were only attacking them. The only other options are to let them steal your stuff, or kill them. Then Archer's so concerned about Nausican response to this.... yeah, I mean if you're not careful they might start attacking your cargo ships or something.
Since Starfleet clearly wasn't protecting them, as the premise of the episode clearly stated this was the first time a Starfleet ship was responding to a distress call, they have every right to defend themselves. Now they probably did take it a bit too far with their counter attack though.