Turnkey investing - where companies have worked it all out for you and you merely deal with the cash end of it - is usually not profitable for the investor. If you hang out around RE investors, they'll caution you on how it seems very alluring because you don't need much knowledge and someone else is managing everything else. But these companies need to make a profit, and so you'll get less of the pie - and they have every incentive to make a deal look better than it is.
The exception is in up and coming neighborhoods.
The article mentions this, but doesn't go into detail: Many of the houses being sold were never on the market. Aggressive marketers contact existing owners and ask if they want to sell, and some small percentage of owners will agree (need cash quickly, etc). Had this not happened, the houses would still not be available as the owner did not intend to put them on the market. It's like complaining that I am screwing up the used car market by asking people if they want to sell their car.
When someone makes $40K+ on a flip, it's almost always the case that the house was in a bad enough shape that a bank wouldn't finance it. So once again, had they not bought and flipped the house, none of the people profiled in the article would have been able to buy it anyway (nor would they want to, being in bad shape and all). They're not stealing houses to make a good profit. They are making it easier for people to buy that house, while they make a profit. It's not a zero sum game.
Almost all flippers hope to sell at market price, and probably at least half list the house at slightly below market price as they need to sell fast. Why? Because most flippers are not using much of their own money. They'll get a hard money loan at, say, 10 or 12% interest to buy the property, and possibly also to fund the repair. Every month they have the house is costing them big bucks. They aim to fix and sell fast to minimize their interest payments. So it's not a case that they are aiming to inflate housing prices. Quite the contrary, it often works out better for them to sell it quicker at a slightly lower than market price.
Now when it comes to investors sweeping up houses and renting them - yeah, that could be a long term problem.
But really: As someone who has an idea on how real estate investing works, my criticism is that one can read this whole article and still not have much of an idea.