The "potential" of embryonic stem cells

Supporters of embryonic stem cell research like to talk at length about the "potential" treatments and cures that could result from it.

Fine. "Potential." Let's keep using that word.

Each embryo that is destroyed to harvest stem cells is a "potential" human life - by the left's standards, that is - it is, in fact, already alive and human: human life. So if "potential" is so important to them, then how do "potential" treatments and cures outweigh "potential" human life? Because the sacrifice of these "potential" lives is worth the "potential" of saving many more lives? Alright, then if it's okay to sacrifice "potential" human life for "potential" treatments and cures, then why isn't it okay to sacrifice non-embryonic human lives for treatments and cures. Let's start performing destructive medical tests on grown men, women and children so that we can try to save the lives of others. Why not, liberals? Isn't the sacrifice worth the "potential?"