The biggest problem with such a clause is that it is hard to define "evil", even if it seems clear to you. Some people think that abortion is evil, so are abortion clinics banned from Json? What about the military and weapon manufacturers? Killing is evil, but you all know how the discourse about the military as national heroes that can't be evil in the US goes. What about a service like X - is it evil? Can you define "evil" for a surveillance tool that brands itself as ad tech?
The clause also states that the product MUST be used for Good, which is a higher bar. I'd imagine most things JSON is used for are fairly morally neutral.
Possibly, I just gave solution to those terms of conduct. Because everyone has other definition of what is evil, to comply they need to follow their morals.