More police can help with theft, possibly with solving murders. It will do almost nothing to prevent terrorist attacks. This airport attack is a prime example of the reason why. You can put large checkpoints everywhere, but there will always be, by definition, a line of people that haven't yet passed the checkpoint and this is where they will attack.
The security theater was specifically about TSA and other untrained (or minimally trained) symbolic gestures. Actual policing is not theater.