Vulcans, for all their talk of infinite diversity in infinite combinations, are frequently depicted as intolerant dicks stuck in their ways instead of being open-minded and adaptable.
That's why, for all their intelligence, they're not very socially adaptable or at ease around other cultures. It wasn't until Valeris that a Vulcan graduated at the top of their Academy class. That's why Vulcans still operate Starfleet ships that are entirely or mostly crewed by Vulcans (USS Intrepid in TOS, USS Hera in TNG ((Geordi's mother's ship had a mostly Vulcan crew)), and USS T'Kumbra in DS9). That's why Spock and his mother experienced so much bigotry and discrimination and why the USS T'Kumbra's captain was a bigot towards humans.
That's why Vulcans are so discriminatory against other Vulcans who won't accept the way of Surak and live a life of logic. If you're not a criminal you are allowed to remain but as a second-class citizen who wouldn't be accepted to the Vulcan Science Academy, the Vulcan Defense Force, or into government. The moment you commit a crime though they're only too willing to put you behind bars where they can "rehabilitate" you, which is more like forced indoctrination because it's the only option available to you if you want to secure an early release.
It's a paranoid remnant from their near-apocalyptic civil war against "those who march beneath the Raptor's wings" AKA what would become the Romulans over 2,000 years ago. Even the more egalitarian Spock immediately adopted a "kill it with fire" approach just like the bigoted Stiles the moment he found out the Romulans were an ancient offshoot of the Vulcan's aggressive colonialist period.
In a way it's similar to how Humans and the Federation they heavily influence have an over-the-top prohibition against genetic engineering that even extends to members of other species serving in Starfleet, all because of their experience in the Eugenics Wars hundreds of years ago.
