Possible, but easily disproved. You can buy the material you need to make various weapons at duty-free shops, restaurants, and so forth on the other side of airport security. You can walk through security with a laptop, which has loads of sharp metal pieces, several lithium ion cells (containing dangerous chemicals that can be used in various ways), etc.

The 9/11 hijackers were not heavily armed. What I described above would have been sufficient for that attack, and the "extra" security at airports does nothing to stop that sort of thing.