And since we're not talking only about therapy, but about enhancement, this risk is too much for us to tolerate.
Any risk is too much.
Others say that as long as the risks are reduced to a level where they are of the same order of magnitude as the risks from natural conception, then they should not disturb us. Just because the human hand is involved in these activities doesn't mean that when bad things happen it's any worse than when bad things happen strictly in the natural realm. These are the two poles of this debate.