The president of the Richmond NAACP, James "J.J." Minor, stated in 2017 talking about something similar that "When you look at something like that, whether you consider it art or not art, lynching is not something that we're in agreement with at all. We do not support any groups that support violence.".
So who finds it offensive? I think the answer there can be the very people who were targeted by such violence. And that some people may not support any group using violent imagery, regardless of the target or intended message. The issue being that using the imagery of lynching, even against hate groups, can normalize or trivialize a horrific form of racial violence.