Sex trade? There is no such thing. How little people understand Thailand or even SE Asia for that matter.
It is just a different form of nightlife. You sit in a bar, have a few drinks with friends, and if something happens between you and a woman working at the bar then so be it. Whether you give this woman money in the morning has nothing to do with the issue. These women do it because they have families to feed and in the Buddhist culture it is the role of the grown up child, usually female, to look after the parents for the remainder of their lives.
Thailand's so called sex trade is no different to Singapore's Orchard Road and Geylang to name a few, Vietnam, Cambodia's Sinahoukville, Philippines Angeles City and Makati in Manila, China, Hong Kong, Seoul, Tokyo, Indonesia, Malaysia and so on. It is not limited there either as you can then include Holland, Belgium, Spain, Portugal, Czech Republic, Poland, Hungary, Bermuda, Mexico, Costa Rica, Honduras, Guatemala, Nicaragua, Belize, Dominican Republic, Brazil etc to the list.
Now what I would like to know is what is so different in taking a girl from a bar in Thailand back to your hotel room as opposed to taking a girl back from a night club in Los Angeles, New York, London, Sydney back to your hotel room? Why is it acceptable for rich white people to have one night stands? Is it because they have a choice? Well guess what? The women in Thailand have a choice as well. Unfortunately they are not as rich as the Hollywood brats or the rest of the women in western society.