I normally avoid these threads but I know you're all dying to hear my opinion so here goes
The pro-group loses me when they say that the only alternatives for uwanted horses are slaughter or starvation.
The anti-group loses me when they speak of government regulation &/or licensing of breeders/owners.
I choose personal responsibility. Each person has the right to do what they think is best & make decisions they can live with. For me that is not breeding my mares, having only the number of horses I can properly keep & keeping them through the end of their days.
I don't show or compete so my horses never lose their usefulness, they remain useless.