You have the same concern I do.
I think the pro-life movement may be putting too many eggs into the "no proven successes" argument against embryonic stem cell research, rather than attacking the moral issue directly.
I, like you, shudder to think what's going to happen if the left is ever able to show any objective success in ESC research.
They refer to “ethical stem cell lines”. There ARE ethical lines available (from adults as well as other elements like umbilical cord stem cells).
That they refer to “ethical” is supposed to give them the upper hand on the argument. There is nothing ethical about their approach. They have co-opted the word.
They can continue down the hope and dream and faith path that stem cells (adult or fetal) will be the cure-all, but they may also lead to higher cancer rates and other bad results.
Which is why experimentation is done.
The main thrust of it seems to be in shielding abortion and fetal farming from restrictions or prohibition.
In Europe, they’ve looked at human-animal hybrids. So they can concoct a “sub-human” race that would also be “ethical” to experiment on. They just don’t GET IT.