It’s important to note however that (1) there are alternatives to mulesing to prevent or reduce the risk of flystrike (see e.g.
Progress on alternatives to mulesing | Autumn 2015 | Sheep Notes newsletter | Newsletters | Support and resources | Agriculture Victoria) and (2) flystrike is only a problem in the first place because sheep have been selectively bred to have thick wool.
Selectively breeding animals to make them more exploitable is cruelty literally built into the DNA of the animal agriculture industries. The huge swollen udders of the dairy cow, the intensive laying cycles of hens, the fast-growing broiler chickens whose legs give way under the weight of their own bodies. Farmers then use these health problems that they're responsible for to justify further brutal practices like mulesing. Another 'corrective' is keeping fast growing broiler breeders on the brink of starvation to prevent them from dying of heart attacks before they reach the age of sexual maturity.