I thought that I might as well answer the OP, considering that it's mine, so:
I personally don't care about whether or not others perform incestuous acts, as long as both parties are consenting adults. If said parties fully understand the social ramifications of said acts, then it isn't my place to tell them that what they're doing is "wrong". That being said, I will never fully understand the motivation behind said acts, as I don't see my siblings in that way.
Biologically, it can be argued that there is a problem with incest. If we are to consider the genetic defects that can arise in offspring, then sure. However, it's been pointed out in this thread that a couple may decide not to have children - two rational adults would surely be able to judge that they shouldn't procreate? If the biological issue is removed, then why exactly is it wrong? It would merely come down to social stigma.
There are circumstances in which one's parents will not approve of their choice of partner, regardless of whether or not it's their sibling. Should you ignore your parents and follow your heart, despite the love and care that they've given you since you were born? In some cultures, parents have such a heavy hand in their children's love lives that any deviation from expectation will be met with severe disapproval - yet is it not the child's choice? Are they not allowed to fall in love, and be happy with the one they love?
The reason that you posit for the occurrence of incestuous acts is silly - a guy that's down on his luck won't suddenly be able to have sex with his sister, just as a similar guy wouldn't be able to pick a random stranger and have sex with her. Incest between two consenting adults still involves two rational parties, I doubt you could just initiate such a relationship because your love life "sucks".