Resources (land, water, feed) used.

Byproducts (manure & litter) generated and how they are managed. See red tide, dead zones in the Gulf, phosphorus overloading in the soils of the eastern shore of Maryland.

As silly as it sounds, cow burps aren't an insignificant source of methane.

Acute pollution around CAFOs and impacts on surrounding communities.

One stat I heard is if everyone adopted our (average American's) meat heavy diet, it would require additional ag land the size of Brazil to support it.

Meat production can be done sustainably (see White Oak Pastures), the near impossible difficulty is doing it at scale to meet the high meat consumption.