Bellatrix and the Cruciatus Curse

So, just the other day, I was thinking about a line that Bellatrix said to Harry when he was trying to perform the Cruciatus Curse:

"You need to mean them, Potter! You need to really want to cause pain... to enjoy it... righteous anger won't hurt me for long... I'll show you how it is done, shall I? I'll give you a lesson —

So, you discover that you need to actually want to cause the person pain in order to perform it sucessfuly. That just proves that Bellatrix is evil because she performs this curse very often. We can find out a lot from this line about Bellatrix's desires. That means that she really wants to inflict pain on Muggle-Borns and "Blood Traitors". Which means, she is truly evil. ( Also, take into consideration that she loves Voldemort but he doesn't love her back. I still can't see why she would love such a weirdo. I guess, since they are evil, they both belong together. Wedding in Askaban! Ha, Ha!)