I'm going to Texas and Sacramento in 3 weeks' time so I'd be expecting to experience what this is all about anyway. But as an outsider looking in, it's not at all a violation of the US' 4th Amendment.
US Constitution's 4th Amendment wrote...
The right of the people to be secure in their persons, houses, papers, and effects, against unreasonable searches and seizures, shall not be violated, and no Warrants shall issue, but upon probable cause, supported by Oath or affirmation, and particularly describing the place to be searched, and the persons or things to be seized.
First, it's authorized by the US government. After all, if something happens on the flight, like terrorist activities or violence in the plane, the US government and the TSA almost always get the flak in the media. So if they're "responsible" for it, then it's right they do something about it. It's sad that the TSA is wound up in a lose-lose situation - damn if they continue with this and damn if illegal materials get in the plane because some schmuck used his body to sneak in some illegal shit.
Let's give the complainers some leeway - the TSA can't fully assure their "pat-down officers" are not sexually motivated while their hands are moving on a passenger's body. And they're usually not medically adept enough to handle, like, urostomy bags.
I suggest that the TSA get privacy booths, and hire female gynecologists for women and male doctors for men to do the pat-downs and full body searches inside those places. Make it a medical thing so that these "we-wont-fly" people won't have any goddamn legal basis to complain anymore of the groping... heck, they can even just scrap the body scanners and have the medical staff handle the searching.
General consensus is, passenger airplanes are now safer. If terrorists can find other places to attack, please do. Let the TSA version for buses, boats, and ships do their thing. But if airplanes are safer now, they're doing their job.