Governments have no reason to buy shares in large companies. It wouldn't the "free market" if government had control over business in such a way. Markets do not require regulation...it was regulation that got business in trouble in the first place. If governments didn't get involved so much, we'd have more small-scale businesses and better competition, rather than favoritism.
To use your food-web analogy, some species would disappear, but that only leaves room for other species to take their place.
To use your food-web analogy, some species would disappear, but that only leaves room for other species to take their place.