Without emotional suppression, they're Romulans and prone to doing bad things.So, we do know in general the reason why Vulcans suppress their emotions is because of how strongly they feel them as opposed to humans correct? Basically, a Vulcan can either have strict mental discipline or else risk falling into paranoia and bloodlust.
The thing is, Spock is only half Vulcan. Presuming he's really roughly halfway between humans and Vulcans, that means one might expect that it's less dangerous to be emotionally uncontrolled for him than an average Vulcan - albeit much more dangerous than for a Human. Hence he can walk the line - and even stumble over it from time to time - without really risking his sanity. He stays under control emotionally more due to his own internalized identity as being "fully Vulcan" than any real need to do so.
Although they never really depicted Romulans as having anger issues in general, in fact most were quite human. Just that one rapey Vulcan in ENT.