Poisoning The Well: indirectly denigrating a position by pre-emptively ridiculing, discrediting or insulting its source. This is a very common form of rhetoric. One way of poisoning the well is to begin a sentence with ‘No one could possibly believe that…’, or ‘Only a fool would argue that…’ or ‘Naïve people believe…’ or a similar phrase.
Here’s a specific example. Imagine a speaker who declares:
‘Only a racist would be opposed to large scale immigration to Britain’
By pre-emptively labelling anyone opposed to large scale immigration a racist, the speaker here leaves very little room for his or her opponent to manoeuvre without appearing to be a racist.
Poisoning the well makes it very difficult for anyone to come back and endorse the view that has been put down in this way. It also insults anyone who holds a different opinion. Add to this that most people prefacing their statements with such phrases know very well that the people they are addressing are inclined to endorse the discredited view, and you can see that this is a devious move in argument. Once you have recognised and named this kind of rhetoric it is fairly easy to identify. The best way to confront it is with a straightforward contradiction of the statement, followed by an explanation of why your position is a reasonable one to hold. You might also consider challenging the speaker to explain why they believe that ‘only a fool’ would argue for this position.