IVF Ethics: Should an Embryo be Rejected Because It's Potentially "Sick"?

The more science provides folks techniques to manage infertility such as through invitro fertilization and then implantation and the more science also provides tools to determine before the embryo is implanted whether or not the embryo is "potentially sick" because it is carrying a serious genetic defect (preimplantation genetic diagnosis), society is faced with further ethical and legal dilemmas. Such a dilemma can be developed from the example above: should prospective parents who desire to have a child by undergoing invitro fertilization be required under law to first have their embryo diagnosed for a genetic defect and if a serious genetic defect is found, they be compelled to reject implantation? Could it be argued that such attempt at diagnosis and subsequent rejection be considered under law and ethics as in the potential child's "best interest"?  And, perhaps in the best interest of the future generations if this embryo was allowed to mature, be born and survive long enough to have its own children? On the other hand, is the general ethical and legal principle of parents "acting in the best interest of their child does not mean choosing the 'best child'"? The expression in quotes is the title of a rebuttal by L.S.Flicker in response to a view set by Malek and Daar discussed in the current April 2012 issue of  American Journal of Bioethics. But what is your thought on this subject?  ..Maurice.