As a professor, are you permitted to prohibit Ph.D. students from joining your research group if you know they have a boy/girlfriend, are married, don't come in on weekends, who don't stay late, etc...?
The professor does not intend to make them work on stuff related to his/her research outside of normal working hours. Rather, the supervisor would like their students to be driven enough to study/read publications and books about topics outside their particular research program during those times.
That way, supposedly, by the time they graduate, they will be very well rounded, and also develop their own research programs in meaningful ways.
Since I observe this behavior with a certain professor I know at a US university, I was wondering if that professor is liable for legal charges, which I could bring up to the dean.
One way I hear about how he "weeds" out the normal people is by telling them how much work it takes to succeed, and gives examples of previous "successful" students, and what their lifestyles were. I suppose he says something like: "this is how much you know from being an undergrad, this is how much you need to know to succeed in this field, here is a humongous list of topics you should know before you can competently do research with me, come back to me when you're ready." But I don't think that's all he does.... I think he intimidates prospective advisees with his demeanor, and so this fact along with his reputation leads to him select students who work day and night everyday.