They do have an impact and it's deluded to think otherwise.
On Mj's facebook page last year on MJ's 6th anniversary there were more than 9000 comments and 471 000 likes.
This year after the child porn story only 4500 comments and 153 000 likes..
I don't want to discuss this again. Album sales numbers, how well Cirque ONE etc does to me demonstrates that those negative stories doesn't have much impact. Like I said a million times before people have already made up their minds about MJ good or bad long long time ago when he was alive. Nothing said and done right now will cause a major shift.
Your logic about facebook likes etc is also flawed. You cannot factually claim any decline was due to the allegations. It is also possible that people's interest in MJ have spiked right after his death and that interest is dropping as time goes on. This is a trend seen with all deceased celebrities. Such as when Elizabeth Taylor died. Suddenly there is a huge interest in her, her popularity becomes really high, her estate makes hundreds of millions but then the following years you see a trend of decline and then it levels.