I think Imus had every right to say what he said, although it was racist. And I think that people have the right to protest him and not listen to him. And, if you notice, the FCC didn't step in. And likewise, MSNBC should post this sick persons ramblings. Just like Mein Kamf should be published, we need these things to understand what is wrong with these people. Ignoring this doesn't make it go away, but showing it, and having people say how horrible it is, might. Would you decry someone posting video of Osama Bin Laden talking about his goals? If no, then why not, he killed thousands more. If yes, then at least you're consistent, but there is still the issue of ignoring the issue. It's alright for you to not want to read those things, I can understand it. I used to be squeamish about seeing video of needles piercing skin. So I never watched movies about junkies or hospitals or anything. That's the thing about censoring media, you aren't choosing for yourself, but others.
MSNBC isn't exploiting the need (although they and other news outlets definitely exploit things a lot), it is offering an outlet for the need. They got a letter from the killer, and they posted it because it's important. Newspapers did the same thing for the Zodiac Killer and countless others. News goes in a paper, that's how it is.
No one should take pleasure in these things, but news isn't about pleasure, it's about knowledge, and the more you know, the less you like it.