I'd go further and say it isn't the job of Western countries to fix corruption. If Putin wants to fleece his people he can take his billions to a European bank.

I'd ask a slightly different set of questions: (1) "Is it good for {country} if {country's corrupt leaders} are able to bank elsewhere?" (2) "Is it good for {bank elsewhere country} if they accept corrupt money?"

(1) is probably not good for that country, but do other countries care? To some extent, this is just colonialism by proxy: extracting wealthy inequitably from a foreign country. Historically, few third party countries take issue with that, when they're the winners.

(2) is where the more interesting point is. Does the country accepting the money net benefit, or net loss? Aka the London banking question in a nutshell.

I'd argue that if money is political power (it is) and corrupt money can't be firewalled (it can't), then it's net loss.

Inevitably and especially if we're talking lifestyle roots (e.g. property, establishing a home, etc), that corrupt money corrodes government and civil systems in the banking country. At minimum, because the wealthy corrupt people bring their expectations and behavior with them!

Yes, good idea. Letting Putin build up power over the last 20 years clearly hasn't caused any problems outside of Russia.

> why should it be the financial sector's job to weigh whether someone is good or bad

In practice though that’s exactly what happens. Banks have to look for transactions that are potentially illegal (including OFAC and AML). And the banks not only report but have to block some of those transactions or they become liable for the initial crime (if it existed at all).