Don't make it sound so childish (most dumb atheists tend to do that; don't be a dumb atheist). Religious folk believe in the existence of the soul, and argue that the soul of an autonomous, rights-imbued individual comes into conception at conception. You don't have to believe in a soul, but it's not a "bad argument" in any way.
it's an argument without evidence, and not worth considering in this situation. they can argue that embryos have souls and I'll argue that animals have even higher value souls, and we should especially not eat them. we'll each bring the same amount of evidence to the table and get nowhere. I'm interested in arguments that are logically consistent and have evidence supporting them.