They join the one Alliance during the Second War, abandon them, ironically get decimated by the Scourge, crawl back into the Alliance, ally themselves with evil beings, and when the small Alliance is destroyed, swear allegiance to the Horde, one of their former greatest enemies.
Blood Elves already have a very low image to the Alliance, yet Lor'themar is planning to betray the Horde they swore loyalty to for them. This really shows Blood Elves have no loyalty.