Off the cuff answer: because he'll get all the girls.

Real answer: I think the problems implicit in cloning are foremost. Assuming we're able to surpass those, we have the inherent ethical issues of bringing a human-like (and possibly more complex/intelligent than humans) being into a very strange environment.

I think we should do it, if we can guarantee a reasonable likelihood that he or she will not endure an inhuman amount of suffering, but there are a lot of ethical issues that have to be addressed. Who will raise him? How hard will we try to give him a "normal" life and prevent his inevitable celebrity from affecting him? How will we determine if he's competent to own property, attend school, live on his own, etc.?