I think Sisko's response to Picard was perfectly reasonable. On one hand it was very unfair to blame Picard for Locutus' actions, but on the other hand, if you were in that battle it's impossible to avoid having those feelings.
Like, if somebody had a stroke while driving a car and then the car ran over your wife. You would know intellectually that it wasn't the person's fault, but you'd still feel like it was.
I think some of the hostile reaction toward Sisko at the beginning was due to the shock of seeing 'Our hero' criticized. Star Trek at that point had been a Starfleet love-fest, so seeing such hostility was unexpected. In retrospect it comes off much better.