Bulverism
Bulverism is a rhetorical fallacy that combines circular reasoning, the genetic fallacy and ad hominem with presumption or condescension. The Bulverist presumes that a speaker's argument is false or invalid and then explains why the speaker made that argument by attacking the speaker or the speaker's motive.
Similar to Antony Flew's "subject/motive shift", Bulverism is a fallacy of irrelevance—one dismisses an argument based solely on the arguer's identity or motive, but these are mere proxies for credibility ; not determinants of an argument's factual validity or truth.
The term Bulverism was coined by C. S. Lewis after an imaginary character to poke fun at a serious error in thinking that, he alleged, frequently occurred in a variety of religious, political, and philosophical debates.
Threat and remedy
The special threat of this fallacy lies in that it applies equally to the person who errs as to that person's opponent. Taken to its logical consequence, it implies that all arguments are unreliable and hence undermines all rational thought. Lewis says, "Until Bulverism is crushed, reason can play no effective part in human affairs. Each side snatches it early as a weapon against the other; but between the two reason itself is discredited."The remedy, according to Lewis, is to accept that some reasoning is not tainted by the reasoner. Some arguments are valid and some conclusions true, regardless of the identity and motives of the one who argues them.