Proving too much

Proving too much, in philosophy, is a logical fallacy which occurs when an argument reaches the desired conclusion in such a way as to make that conclusion only a special case or corollary consequences of a larger, obviously absurd conclusion. It is a fallacy because, if the reasoning were valid, it would hold for the absurd conclusion—the judgement of fallacy is therefore largely dependent on a normative judgement of the "absurd" conclusion. A charge of "proving too much" is thus generally invoked, rightly or wrongly, against normatively-opposed conclusions, and so are often controversial at the time they are made, as in the following examples pertaining to laissez-faire economics and slavery:

Showing that an opponent has proved too much is a form of reductio ad absurdum.

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