Exactly. The goal of a terrorist isn't to "blow up an airplane" per-se, it's to, well, cause terror. The TSA lines do NOTHING to fix the problem, they only move the problem. Any terrorist with half a brain can see that you now just blow your bomb up in the security line. So what do you do, put a security checkpoint in front of the security checkpoint?
Detonating a makeshift suitcase bomb in a security line, you'd be lucky to kill 10 people.
Maybe. I feel like you're underestimating how many people a bomb in the security line could take out. But, I'm no explosives expert, so you may be correct.
And yes, the worst-case scenario is worse for the airplane, but if you're Joe Terrorist, you don't have to achieve the worst-case scenario to be successful. Terrorists commit all sorts of acts that only kill / maim 10s of people. Apparently terrorists believe those acts further their agenda nonetheless.
You can't crash airliner because you can't get into cabin anymore. So most terrorists can do is kill everyone on board, which is the same as to blow a bomb elsewhere (you underestimated potential harm of bomb in security line), and they already are doing that. So those rigorous checkings in airports only hurt normal people, and do nothing for security.
It's TSA checkpoints all the way down...