Good point. But unlike the Vulcans and "those who marched beneath the raptor's wings" who would have destroyed themselves in the civil wars, Romulans did not destroy themselves. They have the same violent emotions as Vulcans do, but obviously they found a different way to deal with them, otherwise they would have killed themselves quickly after having left Vulcan and their would be no Romulan Star Empire.
So what is the mechanism the use?:
My rough sketch of Romulan society is that they channel and direct their emotions upon eternal war via the dogma of unlimited expansion and keep that dogma up with a facistic or facistoid society.
Since Unification we know in addition that there are also Romulans who yearn for a more Vulcanesque approach.