Well, I had no idea when I wrote that one simple sentence "Wool is sustainable, fleece is not", it would lead to such a donnybrook. I don't intend to get into a debate on environmentalism, or whether or not the use of wool is better for the planet. Time will take care of that.
Maybe we'll see, maybe our children.
But it's a fact polypropylene comes from oil, while sheep graze on herbs and forbs and they aren't raised in pens, or barns like cattle or pigs. To try and equate wool production with feedlot agriculture is misleading and just plain wrong.