It (bombing crowds at airports) already has, in 2011, 37 people were killed and 173 injured in an attack at Moscow's Domodedovo International Airport:
As a frequent flyer and having formerly worked with a firm in London providing security to high-net-worth individuals, their residences and places of business, I can assure you that airport security exists for three reasons:
1. Security theatre so the general public can "feel" safe and thus continue flying in ever-greater numbers. This ensures most airlines stay in business (as most of them are leveraged to run on the edge of bankruptcy every day).
2. So that politicians can be seen to be "doing something" about it, ("Quick, here come the voters, everyone look busy.")
3. So that aforementioned politicians can transfer further wealth from the consumer/taxpayer (for they are one and the same) to the military-industrial complex who make and supply all manner of "security" equipment. Most of which can be defeated, (even THz body scanners).
Airport security will stop the casual nutter, but no government, no matter how much technology they gain, or how many of your freedoms they take away, will ever stop any individual suitably comitted to their task.
As for airport queues, it also scares the hell out of me when I see large crowds at the doors of the US "Black Friday" sales, those are easy pickings for the lone wolf or the organised group making simultaneous strikes. Depressing Christmas sales by keeping people away from stores and malls would seriously hurt economies where business balance sheets do indeed "go into the black" during the Christmas shopping spree.