When teaching, I try very hard to keep my personal opinions out of a case, and I think I usually succeed. Even most 5-4 cases that I have strong feelings about, and do not agree with, I can cover neutrally.
But there are a few exceptions, which I warn my students about in advance. One, of course is NFIB v. Sebelius. After giving umpteen book talks, it is hard to separate my views on the case from the facts. Another is Buck v. Bell. I become incensed every time I read the ease with which Holmes tosses aside the case.
But the main one is Kelo. I don’t even pretend I can talk about this case in a neutral manner. I’ve tried and it doesn’t work, so now I give my students fair warning. Every time I read it, I become impassioned at the breadth of what the Court did, and did not do, to property rights (reading this excellent profile of Kelo in the Weekly Standard brought me back).
I suspect some students and professors may be offended by my admission that I have difficult time explaining a few cases without injecting my opinion, and hold it against me. Or some may object that a libertarian law professor unable to teach constitutional law in a neutral manner should not be teaching constitutional law.
I would counter that many, if not most (probably all) professors are subject to the same implicit biases (in one direction or the other), though they may be less cognizant, or willing to admit it. I try to acknowledge my flaws, and address the problem. I find this to be a superior approach to simply pretending they aren’t there.