The horse dewormer thing iirc comes from the fact that ivermectin is a prescription drug, and doctors obviously wouldn't prescribe it for covid. So people resorted to one of the very few ways you could still purchase it: as the horse dewormer variant.

Of course this version is much stronger and intended for horses, not humans. IIRC this led to a few hospitalisations and even deaths.

That's why when people advocate you should take ivermectin, the counter claim is that they're telling you to take horse dewormer, since that's the only way to get it. It's not out of a general 'disrespect' for ivermectin.