RE: Honour Or History?.

If a monument is there to honor someone who did bad things then it is probably a good idea to take it down, especially if the monument is hurting people who were affected by that persons actions.

This answers it all.
It is justified to remove if it was erected in the first place to support a bad thing.
Everyone is flawed, even the past leaders and inventors. If we judged based on that, then we would end up taking down all monuments.