Unless every single access point to the airways scans every single person who enters every single airport, no amount of body scanning will prevent terrorism. The X-ray scanners do a good job of revealing concealed firearms (in addition to dehumanizing and desensitizing people and giving the pervs of Totalitarian Sexual Assault a thrill), but not every airport has them. Once you pass security at one small airport, you have access to "secure" areas at every airport without having to pass through security again. In fact, at many airports you don't have to pass security at all. One person outside security could give a weapon to another person inside security by dropping it off a balcony or sliding it under a rope.
Even if it were possible (AND IT'S NOT!) to build a scanner or train a person to detect every possible combination of substances that could be made to explode, there are ways to hide things from chemical or visual snooping. If someone is intent on dying, what in the world would deter him from swallowing as much explosive material as his stomach could handle? Why stop at swallowing? There's no reason explosives couldn't be surgically implanted. The three ounce rule is as stupid and pointless as the rest, invented by bureaucrats and implemented by mentally retarded thugs. If five or six ounces of some unknown (and unknowable) liquid is explosive, then a couple of terrorists could each carry three ounces and combine it later. Twenty people could board flights from twenty different cities having connecting flights in Chicago or Denver and combine the contents of all their shampoo, conditioner, lotion, and water bottles (that's 12 oz per person) to make 240 oz or just under 2 gallons. Whatever liquid explosive this rule is supposed to guard against, I'll bet that's enough to do the job.
Every object can be made a weapon. Every object. Have you ever broken a CD or DVD? Ceramic mug? A ball-point pen? Banning fingernail clippers from airplanes is moronic. If you want to threaten somebody, there are so many better choices that aren't banned at all.
Totalitarian Sexual Assault
These are all policies invented by manipulative, power-grabbing bureaucrats to placate the simple-minded and acclimate the cattle to being herded. All in the name of security.
Security from what? Sexual molestation? Oh, right! From terrorists. Because everyone knows terrorists would never dream of targeting a large crowd of people all standing closely packed together in an airport lobby. At the risk of alienating a reader or two... How stupid do you have to be to believe that any of this has anything to do with security!?
"Mr. Eloi, please step out of line so Mr. Morlock can feel you up...er...I mean pat you down."
"Well, if it makes us all safer..."