Think about it: this is no different than if the TSA was patting people down as they walk into Walmart. Obviously, causing a plane crash has the potential for disaster, but so does bombing a shopping center. Or a refinery. Is the TSA checking people going in and out of those, or do the companies employ their own security, if needed? I'm betting it's the latter in just about all other cases.
As a consumer, if I feel like I need airlines to offer security, I will tell them about it and then I will refuse to fly on airlines that do not meet my standard. It's not my interest or in the interest of the airlines to have lax security because crashes cost a lot of money and lead to some really bad public opinion (isn't that why ValuJet changed its name?).
I don't have an issue with pat-downs done at airports as much as I have a problem with a third, uninvolved party having inserted itself in the middle to perform the "service". Consumers should have choices. If they don't want to be patted down, and some airline doesn't want to pay for the security, then they should be free to seek each other out and do business - at their own risk (risk of death or injury for the traveler, risk of huge financial liability for the airline).
The choice should belong to the parties involved, not to the TSA.