What I DO hold them responsible for are the series of failures (and hiring of incompetent screning personnel) that allowed the disasters to happen in the first place.
By "them", I assume you are referring to the airlines. However, I would like to point out that it was the government who set the regulations that the security firms were expected to adhere to. When those security firms repeatedly failed to meet those regulations, it should have been the government's responsibility to ground the security firms, rather than blaming (and fining) the airlines for hiring those firms.
Here's another way to look at it. The government is also in charge of regulating airline maintanence. If the airline fails to maintain its aircraft properly or has repeated safety violations, the government has the option of taking away the airline's operating certificate and grounding the airline, thus preventing the customer (the passenger) from doing business with the airline, just like they did when they shut down Valujet for a period of time. The government didn't respond by fining the customer (the passenger.)
But in the case of the security firms, that is exactly what they did. They fined the customer. Since the airline is the one paying the security firms to provide them (the airlines) a service, then that would make the airline the customer. What the government should have done is ground the unacceptable security firms, thus preventing the customer (the airlines) from doing business with the bad security firms.
Expecting the airlines to enforce the government's security regulations woud be the same as expecting the passengers to enforce the government's airline maintainance regulations, IMHO.
There's plenty of blame to go around, but I think you are blaming the wrong party.