The slippery slope fallacy only applies to things that are 'not' shown to logically follow from one another. Saying "We made ɧoɱosɛҳųαƖity legal, therefore, we might make bestiality legal, later." is not a slippery slope fallacy, because making one form a sɛҳuąƖ deviancy legal, would, logically, open up the possibility to make other forms legal as well.