Actually, such reasoning has no place in Constitutional arguments. The Constitution restricts government power regardless of private agreements or organizations. The EMA could disband tomorrow and ratings could be abolished, but the ruling would still be pretty iron-clad precedent that could not be overturned. In legal terms, what you're making is a policy argument; whether the policy of the law would be served or be redundant or whatnot. Policy arguments are summarily discounted by the courts and the Court in constitutional cases. The debate is about the scope of government power, which is not contingent on whether the Court believes the exercise of that power is a good idea but rather on whether it it permissible in the face of Constitutional restrictions.
The ruling speaks at length (from page 15 of the pdf) about how the ESRB and EMA currently fulfil the need this act purported to fill.
The fact remains that you have turned control over to an unaccountable private company (or NPO, same difference) rather than vest control in a government that is duly elected by the people.
If the EMA decide to start pulling video games off the shelves tomorrow (which is expressly provided for in their contract) there's precisely nothing you can do about it. You can't write to your senator, you can't lobby the government, all you can do is write a strongly worded letter to the board of the EMA which they are in no way incentivised to respond to.
I find it odd that America is so fearful of handing power to its elected government, yet so eager to pony over control to a bunch of boardroom executives, I mean, have none of you seen Wall Street?
Yes, the Court outlines several reasons why the law doesn't pass strict scrutiny. But that is a legal sideshow; if the ESRB were to dissolve tomorrow, many other facts could be found to make a similar law fail to pass muster. Strict scrutiny essentially means that if there's any reason, even outlandishly hypothetical ones, why a law might violate the relevant Constitutional Amendment or Clause, the law will fail. I know that seems odd, but, honestly, that's the way it works.
Sure, the ESRB and the MPAA rate stuff for content. But not everything. And it's not *necessary* to partake. Concerted action by consumers or publishers could change the status quo. Government regulations are more pernicious; candidates aren't voted in on one issue, but a host of issues. Even if the majority want something, if the intensity of that desire is insufficient, it will go unmet. But when you're dealing with private entities, they'll react to specific wants of the public much more quickly, theoretically.
Thursday next: I work in financial regulation with Wall Street brokerages. I know exactly what you speak of and I agree that the people should not cede control of the country to corporate oligarchs. But that's not what the ESRB is.