Blood Elves, can they really be trusted? History shows that not one but on many occasions the Blood Elves have sided with the enemy and they will turn on you!
1. The original sect of High Elves fond of magical energies brought the legion to the world for the first time and brought about the sundering of Azeroth. Their Queen Azshara and many Highborne elves were dragged to the depths of the Maelstrom and became the vile Naga. The rest were exiled from the remnants of the Night Elves homeland to what is now the Eastern Kingdoms.
2. After the Second War the Elves left the Alliance, since the Alliance didn't stop the horde from burning down their trees. OH NOES! This same group of social misfits then got killed when the Scourge invaded during the Third War. Then like weaklings many joined Arthas as San'alyn when he necroed them. Pathetic Traitors. Infact it was the Elf Dar'Khan Drathir who helped Arthas level Silvermoon in the first place!
3. Now needing help AGAIN. The Blood Elves cry to the Alliance and the mighty honorable Lord Garithos allowed the Elves back into the Alliance only to be tricked as these same elves were befriending naga! The wise very non racisit Lord Garithos decided an execution of every Elf was in order. The Elves killed their allies to flee with the evil naga to Outland where they met up with Illidan and gave him a brofist.
4. After failing to take the Frozen Throne with Illidan the Blood Elves once again are thinking of switching sides. The Burning Legion promised them big horns and some demon drank, which of course they accepted. Until Kil'Jaeden got sucked down the drain in the Sunwell then their like OH SH*T.
5. Now the Blood Elves left are part of the Horde. However their only alive and with us because they weren't with Kael initially to go on his power trip. But how long will this peace last until the Elves see another opportunity to strike and gain power? It could be happening as we speak! Elves in your guild conspiring against you for power. Who says these Blood Elves won't join Deathwing or even Murlocs should they rise to power?! Strike now and protect your loved ones crush Silvermoon to the ground.
TLDR: Blood Elves. Just say NO