I'd tend to disagree, being an Officer in the Army could be a great career (jet fighter pilot, navy officer, even infantery officer)...
And don't forget, that as a Thai (with a foreign father) you have to do your 2-year military service BUT you can't get promoted !
It seems this is the case, as well, for doctors. A thai doctor, with foreign parent, isn't allowed to work for public hospitals...
It speaks volume about the will of assimilation on the thai side...