The counter argument would be neighbouring Myanmar, which is remarkably underdeveloped for tourists by comparison despite comparable tourist potential (and oil money to invest in infrastructure) because its authoritarian government has historically been boycotted, whereas Thailand's series of mostly authoritarian governments interspersed with elections and coups have usually played the international relations game just well enough to avoid becoming a pariah state.

But it's quite difficult to find a tropical paradise destination with progressive liberal democratic government

You mean a "cheap" tropical paradise with a liberal democratic government. You could always head off to Hawaii if you can afford it, or if you are in Asia, Okinawa or Taiwan.

But for those of us on a more restricted budget, Thailand, Indonesia, and the Philippines provide a better value. Thailand has always pulled through in being worth it for me, especially when prices crash after a coup.