"Appeasement" is a term often abused, thrown about by commentators who seem to have no idea what it actually means. Appeasement and diplomacy are certainly not the same thing -- and given that the Federation kept sending its most powerful ship, the Enterprise-D, to confront the Romulan incursions beyond the Neutral Zone in early TNG, I think it's safe to say that the simple fact that the Federation made a concession to refrain from using their own cloaking devices, does not constitute appeasement.
Indeed. But as you pointed out in another thread, jingoists will call mass slaughter virtuous and paying even a small price for peace appeasement.
Last time this "the enemy is Hitler and everybody who is against us is a Chamberlain" rhetoric has been used in the real world it served as propaganda that justified the rape of a Middle Eastern country.
Let's keep in mind how Trek actually approached the Romulans since the very beginning, with empathy. Empathy doesn't mind you are a weak, tree-huging pacifist, it just means that you try to understand your enemy. First because the opposite, de-humanizing him, just makes it easier for you to commit atrocities against him, second because any good general has to try to think like his enemy does.
Same with the Klingons. They are fucking blood(wine) drinking predators and the last guys you would want over for dinner ... but peaceful coexistence without giving up your ideals (think about the ending of DS9 when Ross and Sisko refuse to celebrate among so many corpses and pour out the bloodwine) is nonetheless possible.