Gene-editing tools just sound too ripe for abuse.
Even though I've been more on the side of caution and restraint regarding CRISPR for about 3-4 years now, I'm not actually worried about anything serious. I think a wrong move at this point could cause such a public backlash that it would set the field back years if not a decade or more so scientists would rather play it safe than take a potential risk or abuse the technology. Besides the list of beneficial single gene traits is miniscule and manipulation of more complex traits is beyond our reach as of now. Also we still don't know what the long term effects of germline modifications could be either in an individual or through generations.
I was a little more worried three years ago but we already spent the entire 2015 having this debate (seemingly fueled by the somewhat hysterical reaction to what happened in China) and after all the conferences around the world last year I think we're headed towards definitive legislation on genome editing in humans, at least as far as the germline is concerned. Japan, India, China, and the US are the areas that need strict legislation the most. Though I understand that people with certain diseases and their families will want to speed things along I'm still confident we'll be cautious before anything else.