"It is clear that scientists have been singled out, since I hear that other ‘simple citizen’, do get their visa in a short time."
Scientists get more scrutiny? What in the world is going on there?
In many lab outside of the US, we are told not to be to verbose about the type of conferences we are going to attend in the US. Words such as "security", "cryptography", "side-channel attacks", "fault injection attacks", etc. must be banned from the application. Instead we just say that we are going to a "computer science conference" or "information processing conference" for instance.
The visa applications of applicants involved in technical or scientific fields may require additional administrative processing. Therefore, applicants who believe they may be affected by this requirement should apply as early as possible.
The fact that this has very bad side effects on technological progress is important, but it's not like the government gives smart people scrutiny because it hates smart people. This behavior is brutally rational if you just look at their primary mission.
I guess it shows what the priorities are. Science? Dangerous! Skinny girls with weird clothing? Come on in!
Did you honestly think that's all they are doing?
They can do anything they want, for as long as they want.
My friend was in the US before he had to go out and get his H1B extended. He was stuck outside the country for about 5 months for "additional scrutiny". He got his undergrad, masters and Ph.D. in the US and worked in the area of chemical engineering + spent working 6 months in middle east on water filtration projects.