This is targeted at Whites, not tourists / migrant workers (legal or illegal) from countries in the region.

(Or is it for those who don't have a work contract in Thailand? A friend in Cambodia went to Thailand once as a tourist funded by his Farang boyfriend and had to show 300 USD as proof of funding.)

20,000 Baht in cash shows nothing more than that you have 20,000 Baht in cash, and if someone does not have that amount (or equal value in another currency, or in his home bank available for withdrawal at an ATM in Thailand - if Thai immigration accepts these, and I was unable to withdraw cash in Indonesia and was glad I brought enough cash) he should really stay home.

For the tourist it is difficult to proof he is not working, and for immigration it is difficult to proof he is working, the 20,000 Baht rule is an easy way around.

They should rather legalize those jobs the Whites are working in. There must be quite a number, and there must be a demand!