So nobody finds evilness sexy?
Weeeeell... I find evilness sexy, sometimes.

But judging by the results of this poll, not too many people agree. that they can't find an eeevil character sexy even if he is sexy... or something.
Me... I don't see why I should feel guilty about it, or make it some sort of a rule that I am not allowed to be attracted to fictional character who are not 'good guys'.

Actually, I find both some fictional bad guys and some good guys attractive. But I think that, in fact, I am essentially attracted to certain characteristics that people can have regardless of how their ethics or actions: looks play a part in it, no doubt, but so do, and even more so, traits like charisma, intelligence, strength, charm, wit, intensity, passion...
Spock is an example of a good guy who is sexy, because he is intelligent, strong, mysterious, charismatic, deep, and all those things that JustKate has already wonderfully described. Unfortunately, too often you'll see writers incapable of creating a convincing and compelling good guy, so the villains and anti-heroes end up being a lot more attractive: a good example is
Heroes, with characters like Peter Petrelli, who is "Idiot Hero" personified, and played by an incredibly bland actor.
Going back to the previous discussion between Rush and PSGarak: Of course, admiration you feel for a person might lead to love, which might lead to a sexual attraction. But I don't think you're going to find someone sexy just because they're heroic. There are plenty of people I admire and respect, but that I don't find sexy.
But, I don't believe that sex appeal is only a matter of physical attractiveness. There are many people who are very good-looking, very pleasing on an aesthetical level, but who do nothing for me. As I said, personality and charisma is at least as important, if not more. To give you an example: I was chatted up in a club by a guy who was very good-looking, but who turned out to be an idiot as soon as he opened his mouth. So, my first thought, before he actually approached me, was "what a good-looking guy", but this soon became irrelevant, and after 5 minutes of a tedious conversation during which I found it difficult not to tell him what a moron he was because of some of the views and attitudes he displayed, I found a way to escape him, and have since avoided him every time I saw him somewhere. On the other hand, one other guy I met proved to be very nice and intelligent and have great taste, and we were good friends for a while, but I didn't find him physically attractive at all - in fact, I found him very ugly, and really was not able to get past that. When he started hitting on me, it felt very uncomfortable, and I had to stop spending time with him. In short: both looks and personality matter. In fact, it is often impossible to separate one from the other. If you find someone attractive because of their figure, it's clearly a physical thing. If you find them attractive because of their e-mails or forum posts, or magazine articles, because of the wit, intelligence, passion or attitude they show through it, it's personality. (And yes, people can find someone sexy because of the way they write and the personality they project through it, even if you haven't meet them and don't know what they look like.) But what if you find them attractive because of the way their eyes glow when they talk, their smile, the way they look at you with piercing eyes, because of the way their voice sounds when they are talking passionately about something ... is it a physical thing, or a matter of personality and attitude? What about people finding someone's accent sexy, or their mannerisms, the way they walk?
Also, personality traits that people find attractive vary: I don't find 'cute', childlike people sexy, which is why I never found Bashir sexy, and why I don't think I'd be attracted to Ezri, if I was interested in women that way. Kira, on the other hand... (but not the Intendant. She annoyed me.)
I don't think I could be attracted to someone I completely despised - they have to have some attractive and admirable qualities you are drawn to. But what if they also have some other traits that make them, well, overall not such a good person? And that's where it becomes more complicated: what if you are aware that someone is far from a wonderful person, but they still have enough attractive qualities to remain interesting and likeable on some level? Let me put it this way: I could never, I never do, find someone sexy, no matter how they looked, if they are a boring idiot. But, let's say, you find someone sexy, not just because they are physically attractive, but also charismatic, smart, funny, articulate, confident, intriguing. However - what if it turns out that they are also completely selfish, immoral, and untrustworthy? Will that make them a less desirable partner for a romantic relationship? Definitely yes (as least as I am concerned - but there are all sorts of people out there, and some might not mind it.) But will it make them less
sexy? I don't think so.