"Firstly there are sniffer dogs as well as bomb detection equipment around every airport I've been to."
I have yet to see them at an American airport. Maybe we have been flying to different places.
"Secondly the reason commercial airlines are different from smaller planes and other bombing targets is because you can use one to kill tens of thousands of people"
Tens of thousands? That's funny, because the largest terrorist attack on American soil involved airplanes and killed about 3000 people.
"You can't do that with a car bomb or crashing a small plane into a large one."
I was replying to someone who claimed that the job of the TSA is to prevent an airline bombing. Crashing a private jet into a commercial jet is a perfectly valid counterexample.
"And the fact you have these incidents at all should tell you that airline security is important."
We had one successful attack, which was extremely well planned and extremely well coordinated. We spend billions of dollars each year on the TSA. Billions of dollars because of an event so rare that we can only point to one occurrence.
Meanwhile, millions of people ride urban transit systems in large cities every day, and none of them are subjected to even the most rudimentary security. A subway train in New York has a capacity of over two thousand people, which is around how many would be on a packed rush hour train. A single terrorist could kill a large number of those people by detonating a powerful enough bomb while the train is going over a bridge or through a river tunnel (and probably in many other places). Yet despite that terrifying possibility, there are no body scanners, no bag X-rays, no shoe removal requirements, and no security lines at subway stations.
You can go ahead and cling to the idea that the TSA's airport security program is keeping us safe. The reality is that their program does almost nothing to promote safety or security; it is all the work that you do not see that is keeping you safe. The body scanners are not even a piece of the puzzle, they are a distraction meant to help people like you feel safe.