Should we edit human embryos' genomes, and if so then how?

I recently received a thoughtful letter from a college student I do not know – I'll call her Claudia* – who took the time to reach out to me with her perspective on heritable genome editing in embryos. The promise of this new technology is that it could fix disease-causing mutations in all cells of the body before damage occurs, and the correction would be passed on to future generations as well. 

My laboratory at Columbia University, New York performs basic research to better understand early human development with the goal of benefiting patients with heritable diseases. Last fall, we published an article in Cell about using CRISPR/Cas9 to potentially correct a blindness-causing mutation in embryos; we discovered that the use of this technology could lead to unintended loss of additional genetic material. Our findings were discussed in national and international media, and had apparently caught Claudia's attention. I reference Claudia's letter here, as I believe that many people share the hopes and concerns she expressed, and because they also in fact align with my own scientific views. 

My...