I'm a brother in Triangle Fraternity for Engineers, Architects and Scientists. (That's the full, formal name... ugly and hard to type. That's why you usually just see "Triangle".)

We are a full member of NIC, and we are a social fraternity, not a professional or service fraternity.

We restrict our membership only to approved technical majors (minor caveat: a man who is enrolled as, for example, a chemical engineer at the time of initiation remains a brother if he changes his degree to English later).

Why do we do this? First of all, these are majors that tend not to have social lives. There's a reason for all sterotypes, generally that there is a grain of truth. One of the predominant reasons they do not get involved in aspects of social life is that the degrees being persued require an unusually high amount of time in study and lab work. Much of Greek life works against people whose time is consumed by academics. In a fraternity where everyone is under the same academic burden, there is no pressure to have social events at academically disadvantageous times (such as parties on Thursday nights... these basically don't happen). There is a reason that most fraternities have few if any math/science/engineering majors.

Two, technical majors have an odd effect on conversations in most social circles. In the Triangle environment, it would not be unusual to have (TRUE STORY) the chip and salsa bowl at a restaurant analyzed as a real world example of Internet network protocols for shared resources. Two people go to dip simultaneously, both back off, pause for random bits of time until one commits, then the other proceeds. Most geeks get a lot of taunting and/or disinterest from non-geeks because geeks continually analyze the world around them. The atmosphere of an all technical fraternity changes that paradigm.

Three, the benefits of knowing lots of people in your profession -- and having lived with such people -- are endless. The Triangle network is no different from any other fraternity network in this respect, save that ours focuses on technical jobs, a resource that wouldn't otherwise exist. A social fraternity creates a fundamentally different bond than a professional society.

Is it discriminatory? Yes. It excludes some people from membership. The question is not whether this is discriminatory, but rather if this is ethical. Discrimination on the basis of race is considered (in this country) unethical because it is not something the person controls, and basics of birth should not cut a person off from access to services. But other types of discrimination are perfectly protected under the First Ammendment freedom of assembly. You have to decide whether "future profession" is more like race or more like creed (which a private organization can discriminate on, and often do -- see Boy Scouts, Mormon church, many political societies, etc).