It is not right to use “Loshon Harah” as an excuse to cover up bad behavior especially where there is a good reason to know, this is not Loshon Harah for the sake of Lashon Harah
People do have a right to decide if they dont want to use niggunim from someone who committed averios even the goyim disapprove of.
If someone was a murderer , but composed beautiful niggunim, wouldnt you want to know and have the right to refuse to sing them
People just seem unwilling to accept the fact that he did cetain averios