I really want to post how both Telaryn AND Levey are wrong (and right) with a mass of new Chronicle™ sources, but I’m away from the PC so [just trust me bro] will do.
Blood elves are still a people with different ideals and moralities. What might they subject themselves as a nation is different to what they accept as a people. Blood Knights being the best example: while the people shunned and spat, literally, on the dark methods employed by former priests, the nation sanctioned them and officialised them enough as to present them to the Horde as a ‘this is what we bring’ card.
In that regard, blood elves do have a history of pursuing dark roads—as long as they lead to results. Yet they stop as soon as their sense of being morally correct/justified fades. It is important to remember that culture and social mannerism don’t/cannot be excplicitly stated in the form of an encyclopedia. For that reason, we deduct from dialogue and interactions.
Overall, it is not out of character for Rommath to do his best in pushing away and eventually exiling Umbric’s cult—but certain members of the people (like, say, my elf) might have different takes on it. Not all Sunfury were evil, and the remnants were accepted back just fine despite waging war on Silvermoon with demons and fel. (-edit: this made it sound like I RP a Sunfury; its an example, not a case)
tl;dr: blood elf society is oppresive and there is no freedom of speech & mind, so you go along with what your leaders decide even though you might disagree
PS: blood elves are 100% not ok with fel and, in fact, it is not at all common/existent in Quel’Thalas. Take a look at the Spellbreaker Guide/Spellstealing and Mana Draining for references to that claim