Most people who oppose stem cell research do so on religious grounds.

Embryonic stem cells are fertilized human eggs. These cells are often destroyed when doing stem cell research.

Many people who are adherents of Christianity and other religions believe that all human life was created by God. Consequently, it is an affront to God to end that life.

It's similar to the abortion debate. These people would prevent research that could benefit millions just because of their personal religious views. It's insanity.