What damage exactly?
The damage that unqualified foreign teachers do to the Thai system is minimal. All the damage is done by the Thais themselves. When they can't produce a curriculum written in English, can't provide basic resources and can't teach their kids to read English to a basic level in Pratom, what hope have we got - qualified or not?
There are schools out there who know what they are doing. Demonstration schools, many international schools know how to teach but this knowledge is not shared at the government school level.
I challenge any fully qualified teacher to teach in a rural govenrment school where 80% can't read and class sizes are in excess of 40 plus. Similarly put an unqualified teacher in a motivated class of 20 in an international school with training, the kids are still going to learn.
I personally know Raphaella (the teacher coming under attack in previous letters) She is outgoing, confident and works hard to give her students a good education. The problem is she teaches 15 classes of 50 plus kids once a week - the vast majority unable to read basic English.
You are wrong to think there is a budget available of 60,000 baht per teacher open to schools. Isaan doesn't need more qualified foreign teachers, it needs to set realistic standards, teach Pratom kids to read and most of all there needs to be a reason for kids to learn English up here.