Anscombe quotation

Here's a quotation from GEM Anscombe's short article "Twenty Opinions Common Among Modern Anglo-American Philosophers" (which contains a list of commonly-held philosophical opinions, each of which is mistaken and can be argued to be such on purely philosophical grounds):

(Error #7) Imaginary cases, which are not physical possibilities for human beings, are of value in considering moral obligation. Thus it may be imagined that a woman gives birth to a puppy or that 'people seeds' float about in the air and may settle and grow on our carpets; this will have a bearing on the rightness of abortion.