On the other hand, Peter Carruthers’s arguments could have been stronger. Carruthers uses the slippery slope fallacy, which is portrayed when he states that if moral rights are denied to humans on certain grounds that they are not rational agents, then that would lead to trigger a chain of events to humans who are rational agents (Carruthers, 1999, p. 114).
Someone who argues that since animals do not have rights, therefore babies do not have rights, therefore there can be no moral objection to the extermination of Jews, Gypsies, gays, and other so-called ‘deviants’, is unlikely to be taken very seriously... (Carruthers, 1999, p. 115).

He is claiming that no slippery slope exists between animals and humans, which is a big statement to make.