McCain isn't in favor or aborting embryos for harvesting cells or for other reasons. He is in favor of using already dead embryonic cells if they will do any good. Same as using cells from your body when you have died.
That is clearly not true. McCain voted to expand research to more embryonic stem cell lines.
Stem Cell Research Enhancement Act; Bill S.5 & H.R.3 ; vote number 2007-127 on Apr 11, 2007
Allows federal funding for research that utilizes human embryonic stem cells, regardless of the date on which the stem cells were derived from a human embryo, provided such embryos:
have been donated from in vitro fertilization clinics;
were created for the purposes of fertility treatment;
were in excess of the needs of the individuals seeking such treatment and would otherwise be discarded; and
were donated by such individuals with written informed consent and without any financial or other inducements.
Those are fetuses. Not dead cells. Fetuses created for the purposes of fertility treatment" are not dead.