I don't agree with the notion Thai bar girls are any worse than any other Thai women with respect to their conduct with foreigners. Like most humans, it's a spectrum.
I do agree many Thais assume any Thai woman with a foreigner is a prostitute. Given they are class-ridden, poorly educated snobs, their opinion is irrelevant to me.
A very common refrain I get from the Thai women I meet is their desire for the company of a foreigner, in preference to a Thai male. Almost invariably, they have had a prior relationship with a Thai.