NAZIs, Green Supremacists. Their core belief is racial purity and superiority to all others.
But I've never seen that even hinted at in the movies.
Maybe not in the movies, but I've somehow gotten the same impression as you, and not generally from novels because I haven't read more than a couple.
The key to the Romulans lies in their past - they are afflicted with a superiority/inferiority complex vis a vis Vulcans because they simultaneously believe that their rejection of Surak is the better path but are afflicted with doubts as long as the Vulcans exist and have a functional society. Since Vulcans' mere existence is a rebuke to them, the Romulans are driven to respond with hostility and attempt to either destroy or re-absorb Vulcan society.
Other races such as humans get into this tussel via being Vulcans' allies. Allying yourself with Vulcans is an endorsement of a sort and therefore also a rebuke to Romulans. If Romulans were "mere" racists, they wouldn't be as interesting as if their attitudes are unique to their specific history. And knowing their neurosis is inherent in their society means that there's no easy way for them to 'reform' and therefore keeps this locked in as a source of dramatic conflict.
We do need all this to be very well spelled out in some future movie or TV series, though. I've gleaned this through inference, and it not only needs to be clarified for the sake of the fans, but could also be the basis for good Rommie-centric drama, particularly given the events of
Trek XI.
In TOS, Mark Lenard's Romulan commander is the one who said in another life he could have called Kirk a friend. He was heroic and honorable.
Calling Rommies racist is probably too strong a word, and yeah I can ironically see Rommies getting along better with humans or other races vs. Vulcans. It's really the Vulcans that push their buttons.