It has great potential and should be researched furhter.
An embryo is a blueprint for a human, nothing more. It's just a cluster of cells, without a brain or indeed any organs at all. It can't feel pain (or anything else) and is no more sentient than a bit of your skin or muscle tissue.
So, I'm all for stem cell research. Of course, a line has to be drawn. Once the inner organs including nerve-cells start developing (and the embryo becomes a fetus, which, while at that point still more resembling a fish than a human, may slowly begin developing conscousness), it is too close to a living human being and from that point onward I have to agree with the nay-sayers. But that still leaves a large windows for use of embryos' tissue for study.
By the way, unfortunately the research on adult stem cells (the ones that don't require an embryo's tissue) isn't as far ahead. Making them fully pluripotent again hasn't worked (so far), so for now we can't solely rely on those, unfortunately.