Even the politicians who favor stem cell research tend to give undue deference to the ridiculous argument that use of embryonic stem cells should be avoided if possible, with this sort of language:

"The involved scientists should be allowed to continue using embryos left over from in vitro fertilization, which would otherwise be destroyed, until such time as they are clearly able to produce stem cells from other sources that achieve the objectives."

At the stage at which they are useful for stem cell production, embryos consist of less than 150 identical cells.   There is not even the beginning of specialization into nerve cells that would give rise to the possibility of personhood.

It would be wrong to *damage* a 150-cell embryo in such a way that it continues to develop into a person but the future person will suffer as a result of the damage.

But there is nothing wrong at all with simply destroying a 150-cell embryo with the consent of the parents (it is no worse than if the embryo had never been made in the first place)