'Can they suffer?'
The question is not 'can they reason?' nor 'can they talk?', but 'can they suffer?'.
Supports
Bentham, Singer · Introduction to the Principles of Morals and Legislation, ch. XVII
- What makes a wrong grave is that it harms someone: pain, fear, deprivation are evils for the one who undergoes them.
- Now a being that can suffer has, by that very fact, an interest in not suffering, a point of view on its existence, no matter whether it reasons or speaks.
- To set that interest aside on the sole ground that its bearer is not of our species is a prejudice of the same form as racism: a speciesism that, without any relevant reason, refuses the .
Therefore So every sentient being enters the moral circle, and where interests are comparable, an equal suffering weighs equally, whether human or animal.
How far does this reasoning convince you?
Not at all
Entirely