You're not factoring in just how much of this international security is driven by US interests(US imposed security requirements for airports servicing flights bound for the US). It's significantly driven by US interests. Domestic flights in several countries I've been to have much less security.

Interestingly though, in Australia you can NOT opt out of the screening machines. They will quarantine and deport you if you refuse to go through them. But then, Australia isn't exactly a bastion of personal liberty when compared to the US.