Certain Christians on the right are correct to recognize that the moral discourse surrounding our politics is largely a cynical point-scoring exercise, an attempt to secure the moral high ground through discrediting opponents, rather than a serious, honest, and humble endeavour.
As such, the discourse is generally more concerned with power than with truth. Extracting admissions of guilt from your political opponents enables you to demand that they act in a chastened and deferential subjection to you as moral arbiter. Almost everyone is playing this game.
Many evangelical Christians are excessively nice people, whose form of faith is itself profoundly oriented around their scrupulosity and overactive consciences. They are also very naïve, and don't understand that they are perfect marks for this game. They can easily be gaslit.
Tell them that they are complicit in the worst atrocities and it is highly likely that they will accept your claims. Accusations of racism are especially powerful here, as given our nations' histories, they can bear genuine measures of guilt.
Their instinctive response, as nice, conformist, conflict averse, and obliging people, when faced with accusations by a person of colour is deference, affirmation, and contrition. Critical assessment of the very often largely unfounded accusations being made is suspended.