What I agree about is that it has been happening for generations. I'm not saying it is right or wrong and I am not bitching about it. Just a fact of life. They burn off rice fields in Lat Krabang outside Bangkok ,Pathum Thani north of Bangkok, outside Buriram, all over Thailand.
Unless the acreage of rice under cultivation has increased at the same rate as the population the amount of smoke should be no different. That Chiang Mai has now become gentrified and the population has increased does not mitigate the fact that the seasonal burning is a fact of life there just like the heat is in Isaan or an upwind pig farm.
Sure there are geographic factors that exacerbate the situation in Chiang Mai but one cannot change that.
If I had respiratory problems or was allergic to smoke I would not move to Chiang Mai. I am sure the vehicle exhaust in Bangkok is as much of a health problem but that is a another story.