You know me, I'm the first to think ill of users :P But I dispute the validity of 'stupidity'. It is not stupidity, it is a lack of education on the subject. I would argue that it is the user's responsibility to understand some of what their computer is doing, much as I would imagine any driver should be aware of really common faults and things that shouldn't be the case on a car, even if they can't strip the engine and rebuild it themselves. THAT, I will argue, is stupid.
That at least is the way I see it for regular users. They do not take responsibility for the way things work that they have control over; those who care already did something about this.
Now, lawmakers. I don't have a lot of faith in lawmakers as far as legislating the internet goes. I don't have much faith in this law for example, other than the fact that it directly affects me to have to deal with it. It is because these people do not understand how the internet works and assume that 1) it is a single united entity and 2) laws can be applied equally everywhere. Of course neither of these are true, and the lawmakers end up screwing something up even if it is with the very best of intentions behind the law.
This law, however ill-implemented it may be, is designed to protect user privacy. DNT and similar measures also put user privacy at the front, though are implemented by people who at least understand some of how the systems work, but even DNT and ilk are flawed because again they put the onus on the developer/site owner.
I'm fully of the belief that there are stupid laws. Most of what comes out of the DHS seems to be flawed, especially with the likes of the TSA... the effectiveness of the measures of actually detecting anything contraband aside, it's guaranteeing that the terrorists win, because now the terrorists do not actually have to do anything and yet everyone is running around on alert and implementing all these measures, which will never be tripped; it's all shutting the gate after the horse has bolted.
Getting down to the point about informing users, informing users is a good thing however you slice it. You're taking responsibility for your end of the bargain, it's not your problem whether users don't bother to read such things. That's one of the flaws with this law is that it's educating users to just click yes, just like Vista/UAC did. You can lead a horse to water, etc.
But if users have access to that information - something not widely normally available - they can make a decision whether to accept cookies or not, or even set up some exclusion rules should they so desire. It's giving the choice and responsibility to the user. You can't make them take that responsibility. But I believe you have to give them the tools to do so - and without laws like this (or, hopefully, better thought out ones), there will never be any reason for site owners to be accountable other than what they 'feel' is right.