No doubt attacking the security line at the airport is a soft target, but no mo where near as soft as a mall. An airport may detect the attacker on the way to the line, you still have to buy a ticket. A mall, no chance. Are the lines a security risk? You bet, it's why I'm glad my GOES account keeps me out of them and thru the quick TSA-Pre line.
But hey, this is all blasphemy anyway, the TSA sucks, Al Qaeda was defeated, and the government desperately wants to keep lying to you so they can look at the outline of someone's body.
And the justifications previously offered for said porno-scanners have turned out to be bogus. The plots mentioned that were disrupted were disrupted by other means such as sigint and humint. So why not continue to invest in the means and methods that work, and cut from the budget the ones that never did?