According to Heathwood’s actualist desire-satisfaction theory, a world in which everyone were prone to desires of bestiality and could satisfy such desires perpetually would be a world better-off than our own.
Heathwood is arguing against the view that base desires (like lust for animal sex, or the desire to terrorize children) are intrinsically defective.
Dr. Cortens is recommending bestiality as a means to living a good life.