"Do you know vampires are basically sterile?"
"You got to be shitting me. No way!!!"
"Yes way."
"Prove it."
"Well, vampires weren't born to kill, they were perfect beings once."
"So, What happened??"
"Immortal beings; corrupted by time. After attaining immortality they indulged in innumerable pleasures and after thousands of years, there was nothing that they hadn't done, there was nothing that could excite them any more. They started growing weary, wanting to die but they couldn't, so instead they started killing and with the death of their prey, experiencing it for themselves."