It's worth assessing why and what this tells us about public opinion. Like many public figures of the past - meaning they've been dead for some time - MLK is no longer a flesh and blood person, but is an icon. Personal animosity has long since subsided, so people no longer evaluate him based on feelings about an actual person, rather what that person stands for.
This shift happens of course not because people changed their minds about him, but because those who formed opinions of him while he was alive - and was a more controversial public figure - are themselves dead. Or if not, getting on in years. Many who form opinions now do so based on what they learn in history books, and the lessons it contains tend to be very positive. It's tough to come out strongly against someone who stood for civil rights and was killed doing so. This is an example of generational politics - something my 2301s hit when we discuss public opinion.
The same thing happens with all sorts of public figures - people like Washington and Lincoln were far more polarizing in their day than they are now. Its worth considering what future opinions about current polarizing figures (maybe W Bush and Obama) might be in the future once those who have personal grudges against them, or affinity towards them are no longer around to answer pollster's questions.
