We may suppose that the money motive might prove the one easiest to detect ........ no point in having it in the bank, and spending above income is very noticeable.
In the liberal cultures developed in the West, many of the erstwhile blackmail levers are much enfeebled:
buggery? no worries; drugs? legal or about to be; alcoholism? who cares ........
Self-motivated and highly educated idealogues may be a rare species in the present climate of cynicism and instant information. The Cambridge spies were a product of their time, an unrepeatable cancer on the body politic I believe. With one significant exception, believing in a creed or a system to the degree required is in short supply. Spies aren't what they used to be.