The problem with hard restrictions like a cap on land ownership is that they would just find a way to circumvent the limit. The best approach is to incentivize them in another direction.
That class of objection is defeatist. Selling unregulated pharmaceuticals is illegal because of the harm is causes. While people may break the law, they at least face consequences and groups that pursue that business are criminal by definition, and face much lower access to capital markets and ability to cause harm.