When fort goes under attack, military repels it without civilian casualties and few soldiers die, there should not be riot as a result.
Has to be said, though, that this doesn't happen in a fortress unless there are a lot of other stressors at work. Dwarves that have been sleeping in meager accommodations, suffering long patrols, eating the same monotonous food or none at all, and then, and only then, does the loss of a good friend set them off into inconsolable grief and rage. It's the last straw, not the sole cause.
I've had mature fortresses where entire squads of legendary dwarves get slaughtered and there's barely a batted eye because everyone is fat, dumb, and happy on their masterwork roasts, legendary dining rooms, and bedrooms like personal palaces.
I do agree, though, that the whole tantrum issue could use a lot more nuance, more like a civil war or insurrection than a hundred unorganized dwarves alone smashing tables or ripping the wings off the geese. But as it is now, after the first two or three years of a fortress, tantrum spirals are usually avoidable unless there's some major, fortress-ending disaster.