I don't think vampires are inherently any more evil than humans. But I do think it's harder for vampires to live ethically, what with the whole drinking blood thing. And a lot of vampires go down bad paths and then it's a whole cycle of them leading other vampires down bad paths (which happens with people too!).
But not all vampires are evil. I try to stop people from dying or getting killed, and I live the best I can. And I do have a soul. All vampires do, though the kind of vampire I am can turn off their emotions. And THAT makes it a lot easier for them to kill people, and it's a bitch to try to deal with.