No, just having 4 motors where one failure is catastrophic.
Quad copters are not more stable then helicopters, in fact it is the opposite. Quad-copters require constant small adjustments several times a second and connot be flown entirely manually. Quad copters are like the F117. they are inherently unstable and thus highly maneuverable. Also Quadcopters rarely have variable pitch propellers and thus cannot auto-rotate making them far more dangerous for passenger transport.