You wouldn't, but the from a void elf point of view, the void poses great danger, and great resources that need to be understood and harnessed to defend the world.
Expelling them from Quel'thlaas for studying and pushing that frontier would viewed as shortsighted and hypocritical given the other allowances they've made for fel and necromancy - while the void has higher priority than all of these because of it's danger and potential.
They'd view taking safeguards to protect the Sunwell vicinity over expulsion as the correct0 decision ot make, but horde affiliations blindsiding them from what's the much bigger priority and threat - the alliance obsession of the horde is not shared in the other faction who seems to at least in general focus on larger threats only having to engage the horde because of its offensive.
What I see is blizzard making enough reason for both void elves to prefer the alliance and blood elves not to want them. But I see most players are taking the blood elves side without question here. Fine, they have their preference, but, there is more to it, than oh the void is dangerous to the Sunwell, therefore it's okay to expel and disregard void elves while be okay with allying with forsaken, and San'layn and other such.
And @
Rhlor - the same blood elves joined the alliance because of those repulsive undead monsters you are a flagging and repulsive Sylvanas' leadership was accepted heartily and even a source of pride for Regent Lord Lor'themar until all reasonable and sane opinion could no longer justify her stance, and then he turned coat.