Lets say you were a really pro-good vampire and refuse to feed no matter the cost because its against your nature, however you don't know of the cure.
That's the thing. Becoming a Vampire (Undead), changes your nature. Hell, there are Vampires so old that they don't even remember being mortal, or what it was like. Like said before, if a Vampire refuses to feed, they go ape[censored] crazy. Just take a look at Lord Lovidicus.
0.5% jesus whats that, like 100 testers? [random guess]
More like 38. Which would explain why there's been so few leaks. Most of the "beta testers" likely aren't even reporting bugs. Plus, with only 38 people in the Beta, it wouldn't exactly be all that hard for Bethesda to narrow down who the leak is.
Anywhere in lore that specifically says the blood has to come from people? They drink from Argonians the same as they drink from Imperials and the rest of the races so why can't the blood be from Skeevers like say if they wanted to roleplay a vampire akin to the "good" vampire from the film Interview with the Vampire.
The blood can come from any source. In TES II: Daggerfall, you needed to kill every 24 hours in order to rest/fast travel, but it didn't need to be a Human/Mer/Beastfolk. It could've been a Rat or even a Ghost. However, remember how Louie didn't stick to the "rat diet" for long in "Interview with the Vampire"?
"Vampires do not consume food as we do, but they must "feed" before they may rest, and they must feed at least once every 24 hours. Unlike lycanthropes, they are not required to feed on the blood of the innocent, but may instead sustain themselves on the blood of any creature. Some of those vampires living within human domains which are close to the various dungeons may be augmenting or even basing their diet on the creatures within those dungeons. This would certainly do wonders to maintain their deception."