My point isn't that it was originally accepted because of the reasons I listed above, but that it is perpetuated and remains acceptable and unquestioned because of that. The fear factor seems like more of a background element, something that very quietly hangs over everyone's heads, probably because the system they established has worked to keep them secret long enough. Obviously it comes to the forefront when something really dangerous happens, like Sarah's transformation or Juniper's near-infection.
Also, another thing I considered is that the werewolves' fears may infact have already been proven unjustified. Not by any real world event, but by the willingness of the hunters to accept the convention. If the werewolves were right in that the discovery of their secret were the worst possible thing to happen, the hunters would be aware of this. And, of anybody, you'd expect people capable of hunting these guys down to be able to capture enough of them alive to prove to the general public that they exist. It becomes a question of why the hunters haven't exposed the werewolves. Either they know/believe that the werewolves are wrong and existing governments would protect them, or they're so delusional that all they care about is keeping the hunt going.
Fear and terror have been really important parts of several cultures, but in pretty much all of those cultures its given birth to powerful, conservative, revenge-driven elements. Particularly in the victims of genocide, where the countries that are formed afterwards are far more paranoid and militaristic, and rightfully so. From their perspective, at least. Werewolves clearly don't have enough of a unified culture for something on that scale, but its still pretty likely that a lot of werewolves favor the convention because otherwise there would be no "legal" way to kill humans within their society.
Anger and rage tend to come after a victim of abuse has recovered and begun to live their lives normally again. From what we've seen, this appears to be the most peaceful werewolf society has been for a while, so the implication is that they've passed the recovery stage.