"Certain people" are exempt, it's true. But some middle class families will be paying more taxes. Perhaps many of them, since they will be helping foot the bill for the tax credit that folks like me are getting and ACA might increase federal health care spending.
To reiterate my specific case, I am not gaining access to medical care via ACA but I am increasing it's cost. Individual cases where ACA does more harm than good do exist. Maybe it is a net good for society, maybe not; but it is reasonable to criticize it for cases like mine.