Disease is fuzzy word, it basically means below some made up bar for healthiness. Take dyslexia as a simple example. That disease can by definition not exist in an illiterate population. We have raised the bar and now they are diseased in need for a cure.
The more we things we cure the higher we will reach and the higher we reach the higher we will raise the bar. I don't think that's a bad thing, but its worth bearing in mind.
Various learning challenges would fall outside a lifetime of suffering, and often such kids have statistically higher IQ. ;)
I think it is more likely people will create synthetic diseases by experimenting on human beings with unique unpredictable gene expression.
He Jiankui already crossed the ethical boundary in 2018... only to discover his best intentions were still nonsense. The GMO kids he helped edit will have a lifetime to figure out if that alteration negatively affected them, and as adults consider how their own children may change.
People may cross the "Primum non nocere" line, but it can never ethically be justified =3