First of all, the government has acted irresponsibly with the powers it already has. Giving them the ability to remotely control our appliances is a terrible idea. We have to fix the problem with the unaccountable government and lack of societal trust before we start even thinking about these sorts of pie-in-the-sky, cooperative efforts which require a VERY high amount of accountability by those in control.
Second of all, even if the government can be trusted, the companies that will build these things will not take security seriously. I won't say maybe; I won't say possibly. Definitely. These things will definitely not be secure. Most companies still think they can just take a half-hearted crack at security, let marketing make it sound impermeable to the masses and act surprised when it comes out that the security was crap in the first place. It's pretty much the industry model at this point.
Finally, and most importantly, it's not even clear that smart meters will have the intended effect, that people adjust usage. As another commenter pointed out, when everyone is using electricity at the same time, there is usually a reason for that.
My fear is that these devices will be forced upon the public (they already are forcing the "smart" meters on us), and when the evidence is gathered that consumers don't adjust usage voluntarily, it will be done by force. And, the government does absolutely nothing to make me think this won't happen. Why should we, the public, accept this?