Neither side in Thailand's class-based political conflict is a paragon of democracy.
My guess is that Thailand's problems with democracy are based around protecting the rights of the losers. Electoral winners get to rule, but the losers don't feel their rights are protected, their views are respected.
If a nation cannot find a way to protect electoral losers, those losers are unlikely to acquiesce in the resultant government. Such a nation is unlikely to succeed at democracy.