oh its selective?
damn
lol.
Seriously, though, think of this to understand:
It's a funeral of a very rich guy. The Rabbi gets up and gets ready to speak. He looks at everyone very seriously and says, "Mr. X had the greatest car on the entire street. Not only were his exhaust pipes huge, there were 2. His house was very nice, and filled with golden saucers and crystal cups. He also had a huge bank account, and managed to save lots of money that he kept safe in the bank. His shoes were also worth more than my suit".
The Rabbi wouldn't get through half of that before people start booing and telling him to talk about the one time he gave charity or him being good to his kids or something, because everyone really knows that all that is fake, and doesn't do more than any other illusion. It's what you are inside that makes any difference, the rest is just filler.
You don't want blood from evil people, because it's not their car or bow-tie that's transmitted, it's a bit from their soul.