Their culture took a major turn with the destruction of the Sunwell, suddenly Fel magic was not only acceptable, but a requirement for them to survive, or so they believed. Demons walk the streets of Silvermoon, a city rebuilt in mere months with the use of that magic, they created large crystals infused with the Fel that were used to empower not only the people (diminishing the effects of the addiction by feeding them the corrupting energies of Fel) but to keep the city functioning.
The extremely corrupting effects of Fel magic combined with their already arrogant views on the world has only twisted them more, xenophobia, fanatic pride in their race and it's accomplishments- imagined or not- gluttony and arrogance has spread and they have turned from the aloof serenity that the High Elves were supposed to stand for and instead embraced a more callous nature to magic and power, perfectly portrayed in how their arcane studies changed focus from the water based spells of the past to the fire and darkness they wield now.
Warlocks are now encouraged to study in open and to share their knowledge as they walk freely on the streets, some take it even further and seeks to take up the mantle of the Blood Magi, further delving in arcane arts that had been forbidden only a few years, the blink of an eyelash for an elf, ago. Magisters oversee the city with the help of their Arcane guardians and magic, monitoring that the people is kept on what they believe is the right path, see these quotes from the Arcane Guardians for an example:
Quote: * Happiness is mandatory, citizen.
* Maintain order within these walls.
* Obey the laws of Silvermoon. Failure to do so will result in termination.
* Remain strong. Kael'thas will -- error -- Lor'themar will lead you to power and glory!
* Do not be disheartened. Silvermoon will remain strong through this course of events.
* Do not disturb the serenity of the city. Peace must be upheld.
It used to simply say that Kael'thas would lead them to
power and glory, now we can assume that they call out Rommath's name for leading the elves, but that's of little importance except as a show of repetitive propaganda. What is more important is the use of the word power, a word which has come to dominate elven culture and at large become the goal and purpose of all elves; they want power, power to put the Sin'dorei at the elevated position they
deserve, power to crush the enemy and simply as a goal of itself.
Kael'thas was viewed as the savior of the blood elves, he was their messiah risen to lead them to the promised land of endless magic, but then he fell. I don't believe that what caused the elves most hurt and surprise was the fact that the he meddled with the Burning Legion, but rather that he become nothing but another insect in the already massive burrow that is the legion. Simply put; he betrayed the Sin'dorei values, he lowered himself from the position of Sun-King and became a servant to another. And he was supposed to be the most prominent of them, their messiah, for this, I think, they hate the Legion almost as fiercely as they hate the Scourge, but their goal for the Legion doesn't have to start and end with it's destruction. I would not be surprised if the elves turn to enslave the entire legion, they are the masters of magic, the lords of Azeroth- all born of the blood and then baptized in the blood of the fallen.
That last sentence references how the Blood Elves are the descendants of the Highborne nobles that escaped from Kalimdor as well as how they were "baptized" by the Scourge as they slaughtered their way to the Sunwell.
Something I wanted to mention before was what Kaghuros said, when the Sunwell was "reawakaned" it was done through holy energies, the remnants of a Naruu used to reignite it. What does this mean for the Blood Elves? As I see it, not much, instead of stealing the light the Blood knights can harnass it through the Sunwell, although how many of them would care? They had the ability to steal it before, so what if the creature they owned was used to give them the Sunwell back, as long as it served their purposes they are content. A few, a very precious few may have changed their ways, but the only proof we have is that Lady Liadrin, after experiencing the Sunwell's recreation felt the love of the Naruu, and then embraced a wish to redeem herself. But what is one proselyte in a nation of heretics?
I hope this helped you some, although I'm not if it answered your question. If anyone got any questions about this, feel free to ask them here or in a PM!