I'm sure it wouldn't be too hard to imagine a scenario where a chain of events results in something catastrophic.
How directionally stable are these jetpacks when one of the motors cuts out?
How often do we hear of parachutists crashing into each other rendering someone unconscious (or killed)?
If one flyer did somehow get caught in a vortex would it be violent enough to render him unconscious?
It might inspire folks to take up aviation (or inspire people to do stupid things with much less preparation).
The benefit to the guys flying the 'wing' is the fantastic thrill of what they are doing against the zero risk to anyone else but themselves.
Isn't that sufficient reason?
Anyway, I won't be flying with Emirates if they think this is 100% safe.