1) mechanics, cleaning crew, and other people who have direct access to the planes do not need to go through security - it's only places visible to passengers where this is done. After all, airplanes are used to smuggle drugs, so the same process can be used to secrete a bomb.
2) additional security and screening costs money, time, and our patience, but there's no evidence that it's effective. A GAO report points out that the TSA expedited purchasing of the full-body scanners without doing anything to ensure it would be better than the existing system. It was done in part as a reaction to the attempted bombing of 25 Dec 2009, but without evidence that the machines would be effective against a repeat of that attack. I also recall a report (perhaps 5 years ago?) saying that penetration testing of post-9/11 security was as easy as pre-9/11 despite the attempts by the TSA at improving it.
3) Another GAO reports highlights that the TSA has done no evaluation of how to improve overall security. For example, a bomb set off in the waiting lines of densely packed airport security, or in Penn Station, would also have a chilling effect on our travel. This attack was done already against El Al's ticket booth in LA. Or consider the hijacking of CanJet Flight 918 where an armed gunman forced his way through security and got on board an airline preparing for takeoff - when the pilots are present but before the doors are secured. Full-body scanners do nothing against this attack.
4) As the GAO and others have reported, people can still smuggle things in their body. These are not detectable by the full-body scanners. With enough people in collusion, that is sufficient to get the parts for a bomb through security.
If it's impossible to keep drugs out of prison, with 24-hour observation and multiple levels of walls and barriers, it's not going to be possible to keep a bomb or weapon out of a plane. The goal is to reduce the likelihood, but there's no evidence that the full-body scanners make a real difference. Instead, they waste money, waste time, waste patience, and inure travelers to yet more intrusions on their personal life.
Therefore my annoyance comes from being told to do things which are meaningless and ineffective, and perhaps even detrimental to overall security.