Answer:
Slippery slope.
Explanation:
A fallacy is demonstrated as the flaw or error in the reasoning of the argument which makes it unsound and invalid.
Slippery slope fallacy is described as the flaw in an argument that falsely asserts a minor or small step leading to a series of major events that are quite significant to a particular consequence.
As per the description, the given argument displays 'slippery slope' fallacy as the minor event('the animal-rights activists get their foot in the door') leading to a series of events('if they sell us on the idea that animals have rights, next...insects') which would bring significant yet unintended consequences(' will lead to the decimation of our agricultural industry', 'starvation of human race will follow'). Thus, the argument fails logically to establish the appropriate cause leading to the significant effect and hence, displays 'slippery slope' fallacy.
