well, let's see. I don;t know. Maybe catching him before he does it? I haven't answered my own question. Neither have you.
How does checking an ID stop him? It doesn't. And since the presented ID's are not being recorded and used to check against watch lists, for instance, the ID check is useless.
He is still going to detonate and kill people.
Do you think that terrorists carry IDs that say "I'm a member of Al Qaeda - I am carrying a bomb but if you arrest me within 20 seconds I will not detonate it."
A cursory look at an ID isn't going to protect anything terrorist related.