If you want make your baby smarter, taller, or more handsome, it's not so easy because these traits involve 1000s of genes.
For this reason I do not think that curying diseases will lead to designer babies.
Well, you're wrong. Where is the line drawn for what constitutes a disease? Retardation? Autism? Eventually every child below, say, 130 IQ will be considered disabled and unable to find work.
Apply this to every other trait: cardiovascular health, strength, height, vision, etc. All forms of weakness can be considered a disease. The end product of eugenics is that mankind will be made into a docile and fragile monoculture.
>If you want make your baby smarter, taller, or more handsome, it's not so easy because these traits involve 1000s of genes.
And? it's obvious that the technology will eventually be capable of this, just not all at once. It starts with single-gene mutations, then it will be 10's of genes, and then hundreds and thousands.
That is the slippery slope: there is absolutely nothing about your reasoning that prevents one step from leading to another.
There's no inherent metaphysical worth in being on any particular level of strength, height etc., so we can spread whatever is the most convenient. I think arguments against (that I see being made) ultimately devolve into some magical thinking and a priori thing bad. (I am glad to be shown otherwise.) In fact we are already messing with human fertility in possibly unsustainable ways, so maybe more tools are needed as a part of the way out.
Of course there is political execution, corruption etc., but I don't see it any different from other technological challenges that civilization has dealt with. I.e. we need better politics but the tech is not at fault. Gene editing is isolated interventions, so it's in that detail more manageable than for example mass surveillance which is hidden and continuous.
One more esoteric argument is that we cannot socially agree on what traits are desirable. The ‘The Twenty-first Voyage of Ijon Tichy’ scenario. So opposite to "monoculture" in a way. But I don't see people expanding on that.