Evangelicals espouse Biblical literalism to the point that they reject not only science, but intellectualism in general. They attack education whenever it disagrees with their views, and as an educator, this is appalling. Their solution to a conflict with their views is not to do further research and consider that perhaps their views might be wrong, but rather to close their minds to additional information and to attempt to "protect" society from these conflicting facts by denying their existence, and by squashing further investigation for everyone.
Does this deserve disdain? Yes. Because their very presence in an institution of higher learning proves that they are hypocrites. They are using the university to get those magic letters that grants them a better job and better pay, but they are only going through the motions. They don't want to be educated. They don't want to be exposed to dangerous facts. They are the very antithesis of higher education. So, yes, I say again, they deserve disdain.
Does this mean that I discriminate against evangelical students in my classes? No. Unless they tell me, I have no idea who is and who isn't an evangelical. I don't teach a subject that forces them to directly confront their beliefs (unless you want to count the value of π). But there are many other fields in which students are required to confront beliefs carried over from four thousand years ago, and when that happens, refusing to accept reality is certainly grounds for failing a course in which they are unwilling to understand the material. And frankly, aping the professor and merely regurgitating information without thinking about it should be considered fair grounds for failure, if only because the student has learned nothing except how to lie well.