There's plenty of noble points that can be made about not playing God and handling the essence of life responsibly, and so on, but I think there's also some risk of losing sight of the fact that we're not just doing this for fun- we're doing it because people are literally dying and we're trying to stop it. If you have a parent or a child of yours that gets cancer, you're not going to be terribly concerned that the cure was created using CRISPR, or that there isn't 100% certainty about what all the side-effects could be.

The fact is that there is not a single medical treatment available that is fully understood; we regularly learn new things about aspirin, which is one of the most studied medications ever, and which has been in use in some form or another since a medieval wise woman chewed on some willow bark. Applying the sort of standards you're trying to hold genetic engineering to would take away every tool in the medical repertoire, aside from perhaps the bone-saw.