Just because God tells humans to multiply, it does not follow that IVF or any other form of reproduction is ethical. That it is a non sequitur. If we were to use your reasoning, the rapist could use this same divine command to justify his actions when such actions led to conception. The immorality of IVF is not principally based on the fact that many embryos are lost in the process. Even if all the embryos could always be saved, IVF would still be unethical, for other reasons.
When you spend a lifetime with your child, that one act of sex that preceded him becomes as important as a mote of dust.
Take that kind of reasoning and apply it to rape, and you will quickly see that it fails. Whether or not the importance of the manner in which a child was conceived becomes smaller in one's mind as the child grows up and one becomes further removed from it in time, that does not change the morality of the act. If the child was conceived by an act of rape, the act of rape was still wrong, no matter how important or unimportant that seems 30 years later. The question is not how important it is to do what is ethical. The question is whether IVF is ethical.
- A8
What other reasons?