You probably think the pro-science side is weak

I don't think the "sides" here will have a "pro-science" and "anti-science" labels. The dispute is going to be, as usual, about power, money, and values.

Do you want to be specific about what failure modes you forsee?

Sure. CASSANDRA MODE! X-)

I foresee first a blank prohibition based on the "we have a nice business going on here, this shit sound scary and, worse, capable of inducing serious socio-political changes -- let's just forbid it all". Then I foresee a gray market developing for the children of the rich and famous and the regulators turning a blind eye to it. Then I foresee the gray market becoming so widespread it will become impossible to ignore it any more, so the regulators will come up with regulations to safeguard public safety and morality. These will initially take the negative form as bans on certain types of modifications. Eventually they will add mandatory modifications ("This is just like vaccines! Are you anti-science?! Don't you want the best for your children?") which is where things will start to get really iffy. If the society manages to get through this without the wheels flying off (I'm not holding my breath) we'll probably get to the "everything not forbidden is mandatory" stage.

Is that specific enough?