Certain chemical liquids and/or gels that are harmless by themselves can be turned into explosives when combined. The thought is that someone could bring in chemical A inside, say, a toothpaste tube, combine it with chemical B brought in disguised as a bottle of shampoo, and make an explosive and bring an aircraft down. The regulation aims to keep the total quantity of material available to an individual, or small group of people, small enough to adequately reduce the effectiveness of such an explosive made on an aircraft.
Steve, this isn't so much directed as you as it is a generalized reply to try and provide some information.
It doesn't even have to be disguised. Toothpaste contains propylene glycol which is one of a few components needed to make trimethylolethane trinitrate, similar to nitroglycerin.
Nitric acid for this fun solution can be found in fertilizers.
Sulfuric acids can be found in dishwasher and laundry detergents.
With those 3 ingredients you have most of the core structure for this explosive.
Another one, nitric acid mixed with cooled acetone to 10 below C is extremely unstable. A little dry ice, a normal bottle of acetone (12 oz) and an equal amount of nitric acid and you can blow up a closet.
The point is, it isn't a joke, it is real and the restrictions have reasons. I know only basic chemistry and have google, took me 10 minutes to compile this. Anyone with an average IQ and a couple hours of time can make all kind of explosives with household items. Imagine what a chemistry major with a genius IQ could do with years of research... That is what we are defending against.
Mind you, I have spoke on my disagreement with some of their policies, and the 3 oz rule is one of them. But I don't think it is worthless, just frusterating. The employees may be a joke, but the people the write these rules know the dangers, they have purpose, and the threat does exist.