You cannot have true security. You can have acceptable security. The law of diminishing returns kicks very hard after a point.
Basically you should aim to keep terrorism the least of the risks for the society but to accept it as a non zero.
But the moment less people are dying from terrorism than lets say random obscure health condition then the money and resources are better invested elsewhere.
The point isn't the number of people dying. Its the chilling effect. Travel was way down after 9/11 due to fear. That has a much bigger economic effect than just the deaths.
In the 1970s there was no airport security. Airliners believed it would be cheaper to just pay off plane hijackers. That was before those hijackers started flying them into skyscrapers.
The lower airline travel isn't just from fear; it's also from the additional time and hassles of security.
. . . although after many years of not flying, in the past 2 months I've gone through security about 10 times and it's always been pleasant and professional and quick.
Basically you should aim to keep terrorism the least of the risks for the society but to accept it as a non zero.
But the moment less people are dying from terrorism than lets say random obscure health condition then the money and resources are better invested elsewhere.