I have been putting a lot of thought into this and I'd figure I'd start a discussion on it and share my thoughts.

So, not only do we see this kind of behavior; that being vampire's have a superiority complex, believe themselves to be demi gods, look down on mortals, refer to people in general as mortals, and some times greedy about more power. We see this in movies and as well......TES quite a bit. Lord Harkon and other vampire's we fight act in this manner.

According to Serana. Lord Harkon and her mother, Valerica got a long before they were blessed or turned by Molag Bal. Than came the fighting, than came Lord Harkon's lust for more power and for that prophesy about blotting out the sun and vampires living in harmony on Nirn as a whole. This reminds me of that movie Daybreakers where the Vampire's food source, and in TES terms....Mortals dried up and left the Vampire's suffering from Blood Lust and the thirst. We all know that Lord Harkon was unstable before.

Now back to the behavior aspect. I do believe it does affect people in TES because I remember Movarth in the story Immortal Blood. He killed vampires...in fact he enjoyed killing them, but yet we see him in Skyrim as one and of course....as a thin blooded vampire as Lord Harkon would call him. He's not very friendly. Turns out it seems he is the leader of a small coven hiding out in a cave.

It seems vampirism does cause individuals to be influenced differently. Some may not be affected by the vampiric blood as others are. Now I believe that maybe since vampire's spawned from Molag Bal's blood that they become this way over time as they get older or sooner.

Now since the blood came from Molag Bal. Some part of him must be a part of that individual. Perhaps individuals inherit a small part of Molag Bal's malice?

Of course there are vampires like Valerica and Serana who remain their own person and don't go crazy or lust for more and more power. But I do believe that vampiric blood not only makes one stay fresh, but I also think it changes them as a person in general.

But this is merely my theory on the blood. I believe that not only does it affect the body, but it must change the individuals mind as well considering that too is a part of the body. Doesn't the mind have to adapt to the body's needs? Say if the vampire needs blood, is the mind influenced by that as well since it is a need for nourishment ? Although not all vampires need it to survive.