You know, this isn’t the greatest argument. Horse Dewormer is an antiparasitic. It’s legitimately used by people as an anti-parasitic (also, dogs, and other animals, not just horses).
www.drugs.com/ivermectin.html

You can definitely say “joe rogan thinks an anti-parasitic drug works on viruses.” but calling it a “horse dewormer” is ignoring the fact that it’s actually also a “people dewormer.”