I get what you are saying and that you are posing this for argument sake, which is great because it's something people worry about. My counter argument would be: Since 2007 there have been millions (around 4-6 million I think) of foreclosures which created a flood of inventory all at once, resulting in artificially low prices. The big boys did play a roll in accelerating the correction in certain markets, but only marginally (in my opinion) until that inventory dried up and prices returned to normal. They have since stopped buying in large volume and prices are still rising as they would in a healthy market.
Reiterating @Fey Chen 's point; Let's assume that the "big boys" own 20,000 homes in Atlanta and, for whatever reason, decided to evict 20,000 families so they could sell them all at once. Atlanta's inventory would rise by ~50% for a few months until that inventory was absorbed; prices WOULD drop a bit, but, assuming all other market conditions were healthy, don't you think they would correct fairly quickly once inventory levels returned to normal?
In my humble opinion, these guys don't hold nearly enough market share to move the needle for any meaningful length of time, even if they had a reason to.