If you're being paid through an account back home and are working in a villa you've rented, it would be very hard for them to prove you're actually there working full time, would it not?
You really would not want to end up in a debate with Thai immigration on this topic either, no matter if they have proof or not.
Outdated legislation which is no longer enforced is common everywhere. For example Alabama has a homophobic law which says this must be included in every sex education program:
"homosexuality is not a lifestyle acceptable to the general public and that homosexual conduct is a criminal offense under the laws of the state."
http://codes.lp.findlaw.com/alcode/16/40A/16-40A-2
Illegal != Enforceable
REAL tourists have a HUGE effect on the economy.
REAL businesses that make the effort to operate legally, employ local staff, pay taxes, etc, have an effect on the economy.