A sufficiently malicious, motivated, and suicidal (or misled) actor absolutely could use an explosive or biological weapon to attack an airport, essentially regardless of the on-premises security posture. For explosives, one would simply detonate their bomb IN the security line on a busy day. For biologicals, one would simply infect themselves first, then spend the day at the airport waiting for a plane. I continue to be baffled why we don't hear more of such attacks.
