this thing about professors welcoming disagreement from their students is actually pretty difficult, more difficult than i've made it appear, perhaps. i don't teach grad students, though i have here or there, and i'd say i rarely run into an undergrad who i would think presents a serious challenge to my point of view. like i say, philosophical prodigies are exceedingly rare, because you have to know a lot - it takes years of study - to really be in the debate. also undergrads tend to be kind of passive overall, and you're not usually reading very extended treatments etc. but i've been a grad student and had problems in this regard and i'm in the culture where this is often a question. i've seen all the possible responses.

at any rate, one thing is that you have the opinions you do and that means that you regard those opinions as the right opinions. and if you're in my line of work, you've spent years or decades developing lines of argument for these views, which you obviously regard as superior to those of your rivals for their contrasting views (though if you're a reasonable person you also wonder whether your arguments are as good as you think, etc). so it can be hard to see the quality of another argument, especially from someone who's not quite as thoroughly in the question as you obviously are. now also people like, let's say, kuhn, were constantly embattled. they were attacked all the time and they had to fight for their ideas (rorty too, come to that). so they're already in a defensive crouch and they are probably sick of most of the obvious moves. (on the other hand, though, you are in a serious power-differential with your own students, and the actual current threats are people at your own level of eminence, and you just need to be aware of the power you actually have. it's never right simply to crush people whose careers depend on you.)

also people like that have a stake in regarding their ideas as the beginning or the avant-garde of a movement, as progress, as things people will come to eventually (thus also of course recognizing your importance). so if grad students come at you with an attempt at refutation, you take them to be reactionaries. you might not know it exactly, but you are trying to gather followers; you think you're right and you want the right to prevail. this was absolutely explicit in rorty: he had a whole history of human thought, and he thought he'd discerned its direction, and he was pushing it along. he lined up a history of progressive figures who'd had partial insights and of course in a certain sense this culminated in his work. the very worst example is hegel, who i think believed that the world-spirit had reached in culmination of self-consciousness right there in his own work. but most people in philosophy who are not primarily historians - or would like to regard themselves as major figures - have something like this sense. (i have always written as though i was a major figure, even though i am one of the few people who thinks i might be.)

so it is a sticky difficult matter to see two students of equal knowledge and intellectual ability as equal where one agrees and one doesn't. one is progressive and sees and one is reactionary and doesn't. obviously the one who does is right and also easier to talk to and more ego-gratifying. it's not that you want to judge people wrongly; it's that the lens can't help but distort. i too am subject to this. edge toward my point of view, or add to it, and my heart goes: yes!

but it is really really important to have some tendency or ability to step back from that, though this will always be limited. you have to affirm consciously a commitment to pluralism, and you have to worry constantly that your ego is engaged one way or the other. some people are extremely bad at doing that (such as kuhn as portrayed by morris). no one can do it perfectly. but i did have a fairly good experience with rorty as i attacked and attacked. and i wasn't completely right, and my arguments were half-formed or were the same old realist arguments that he'd been dealing with for decades. but he read carefully, helped me improve, sometimes took pleasure in the challenge. that speaks incredibly well for him. i know i wasn't his favorite student ever; how could i be? (he always mentioned robert brandom, who i'd say has more than paid off on that assessment.) but he let me write a dissertation, get a degree, and he wrote me a letter of rec. that is a pretty good model of how to behave.

(there are completely different models of education, of course, that reverse-value pluralism or a critical test of ideas. the, um, german model. you have to serve an apprenticeship; get so far inside the ideas of your professor that you know them as well as, and in the way that, he does; then you're ready. i've seen the cult of the herr professor in action. i'll name names: charles scott and john sallis (whose persons and followerships i knew at vanderbilt when i was on a post-doc there), but also maybe cora diamond at virginia when i was in grad school, who wanted to make you a grand-acolyte of wittgenstein. let's just leave this approach entirely out of consideration, though i never had any luck in actually ripping it to shreds at first hand, and among grad students the follower is always more common than the critic.)