It is the inconsistency a lot of people object to. Sometimes we have to take shoes off, sometimes not, same with belts. Entering NZ I had to take my wallet, checkbook etc out of my pockets. Leaving UK I've seen people had to take off flip-flops with no room for concealment. Coming back from Greece, no shoe or belt check, bottles of water often waved through.

RtS
(haven't been through a full body scanner yet, I can imagine the vomiting from the viewing room if I did!)