I'd actually like to get into the definition of a family bond. What exactly is it and where does it start, and where does it end? If you know you have the same blood as that person and feel closer to him/her than with the rest of the world - does that fall under "family bonds"? If you just feel closer to that person because you know he/she is blood related and actually love him/her even more because of that, but feel NO other bond of any type, is it really that wrong?
As far as I've understood, most countries outlaw incest not because of the arguably disturbing love the two individuals feel for each other, but because of certain effects of inbreeding. That, in theory, both strains the country and the society quite a bit, so such relationships are frowned upon severely.
If you, however, practice safe sex and don't end up breeding, doesn't that just completely abide the law?
For the last part, you have to realise that incest is an aggregate of both that bond I have mentioned in the first paragraph, and pure natural love - and that makes it unique and appealing to people who fantasize about it.