It's a bit of a street hustle to invent a condition where someone has to defend slavery to reason about another idea. I'll give this line of criticism some standing when its proponents lift a finger to type something against its current incarnations and its beneficiaries. It's like me saying it's impossible to consider your argument seriously because it was typed on the backs of Congolese child laborers in cobalt mines and unless your comment justifies their suffering, you might as well be chaining them there yourself. It a trolling tactic for policing weak minds.