I guess this applies to all crimes, even major ones likes murder and child abuse. We can monitor everyone all the time, or make sacrifices to live in a more free society.

If you think the optimal amount of crime is greater than zero, at some point we are clearly using different applications of the word optimal. One person is talking about the level under the optimal “solution”, while the other is talking about one constraint that still must be balanced against other constraints. The optimal amount of fraud spending is zero, but then we’d be left with a ton of fraud.

Exactly. The optimum amount of fraud is really zero. But in order to achieve last 0.00001% you may end up screwing up experience for about 99% of your customers by asking them to 10-factor auth and what not.