US Embassy has terrible reputation among Thai visa applicants

The letter from the US Embassy makes it sound as if the only thing one has to do to gain a visa is to show up with a valid passport at the embassy. The truth is just the opposite. The US Embassy has a terrible reputation among Thai people I know who’ve requested visas to either visit or study in the US. 
Thai female friends have requested visas only to be told at their interview that their reasons for visiting aren’t credible and that they are undoubtedly going to the US to work as prostitutes. These are Thai students from good families who only want to visit and/or study there. I know of young Thais who have had letters from members of the US Congress supporting their visit and yet were still refused a visa and told, “[Congress] doesn’t make the decision, I do”. I’ve also heard from Thais who have received European tourist visas quickly, but then found difficulty getting a visa for the US, and at a higher cost.
Most countries I’m familiar with have a set standard for issuing visas, but the US has no such system. The decision is based solely on the interviewer. If that interviewer has had a rough day or is otherwise in a bad mood (a fight with the wife, etc) there is nothing to stop them from refusing any and all visa applications.
When I brought this up with the US Embassy and State Department as a US citizen, I got no response at all. And when I brought it up with my Congressman, I was told they had received numerous complaints about US Embassies around the world and that they are “not accountable for their actions” in issuing visas.
Something needs to be done to bring issuance of US visas under proper rules and regulations, rather than leaving it to the whim of people at the embassy.
A Disgruntled American