Oh it's all over the abortion threads. The question that comes up again and again is: if it's a sin to abort an embryo why is it not a sin to spill your seed on the ground?
That sounds more like a religious argument than a scientific one and has nothing whatsoever to do with killing a living human being. It is hard to get people to change their religious beliefs...as evidenced here on the environment forum...people who believe in man made climate change believe with religious fervor...they have to believe because there is precious little empirical evidence to actually create informed certainty. You can point out the failures of the hypothesis, ask for observed, measured data that they can't produce over and over again, point out the obvious flaws in the models, etc. etc. etc...and they continue to believe...
Belief in something that can't be demonstrated with observations and measurements simply is not rational...I of course it isn't proper to say that such beliefs are wrong...especially in spiritual matters where faith and belief are really all there is...even atheists "believe" in something that they can no more prove than religious zealots...in matters of science, however, and arguments on scientific topics, faith and belief simply are not rational..if you can't provide observed, measured evidence in sufficient quantity to back up your belief, then you really don't hold a scientifically valid position