Well I lived there, not just in Bangkok but spent some time in Chiang Mai and Khon Kaen. It is the westerners who exploit the locals by removing them from their squalor by paying them for sex and other deviances, this industry is exclusive to Bangkok. Most of the snakes eat the rats in Bangkok, the vast majority of rats that do exist are located only in areas such as Sukhumvit, an area filled with tourists and other westerners. Overcrowding will always lead to a build up of filth, I've seen rats in Melbourne's CBD too, hardly a densely populated place in comparison to Bangkok.