One non-religious reason against stem cell research.
There isn't one. ...but this isn't what people are actually arguing about.
See, if we did the smart thing and collected stem cells from fat tissue instead of embryos, no one would/should be complaining. And I read this scientific knowledge first in Wired way back in 2010! (Seriously, it's a great article: All Natural: Why Breasts Are the Key to the Future of Regenerative Medicine and has been out for more than half a decade.) If you took the time to look at the science, you would find that fat is a ridiculously better source for stem cells than unborn human babies (aka "fetus"):
There is roughly one adipose stem cell per 100 fat cells. (By comparison, bone marrow contains one per 250,000 to 400,000 cells.)
So go donate some of your fat for science (I'm willing!) and let's super-power stem cell research.
What people complain about is the use of stem cells from aborted children (and not just for the obvious scientific reasons).
...which brings us to the non-religious reason against safe abortions.
Filmmaker, Writer, Empty Nester