Any "Catholic" who publicly backs EMBRYONIC stem cell research should be excommunicated pronto.
Properly speaking it should not take a formal excommunication--all it should take is the priests being aware of the person's stance.
But seeing that the MO ballot initiative, misnamed the 'stem cell research initiative' is about human cloning, any supporters of the measure in your communion (as among us Orthodox) should be regarded as self-excommunicated. (Hence my correction to 'apostates.')