The problem with this sentence is that "evil" can mean so many different things -- some of them fit well to some people, some of them are strawman versions.
We need to be more specific. Otherwise it's easy to get into a "reversed stupidity" pattern, where we notice that the strawman version of the argument is obviously wrong, and therefore... no people are morally worse (e.g. more likely to cause others harm, even without personal benefit) than others.
Imposing "maximum possible harm on their unwitting victims" sounds pretty unambiguously evil. If you can come up with a reasonable definition that disagrees, feel try to type it out.
http://www.plosone.org/article/info:doi/10.1371/journal.pone.0041812
Here is a rather curious paper describing psychology researchers' attempts to investigate "spitefulness" - I think they define spitefulness roughly as "hurting others without any benefit to oneself". References the Stanford Prison Experiment. Concludes, more or less, that some people are spiteful, sometimes.
I have many reservations about the methodology used in this experiment (main one: not sure if the entire process really reflects any real-world motivations, and hence results might not mean much), but I thought it might be of interest to people on this site. Also, of the 30-odd references cited at the end of the paper some sound rather interesting and many are available online.