Calling it horse dewormer is either propaganda, or just a plain bad faith argument. The inventors of this drug won a Nobel prize for the discovery and it’s use in humans. It’s recognized as an essential drug.
But people are purchasing the horse version. What is the conversion between a 50 mg tables and a tube of paste for a 1200 lb animal? By using the wrong formulation you run the risk of liver damage due to an overdose of ivermectin.
That's a straw man. These people are of course doing something dangerous but mainstream newspapers are routinely calling doctor prescribed Ivermectin 'horse dewormer'. Both 'camps' treatment of this subject has been a real low water mark and it looks like the science might be as well.