I see this as a predominantly moral issue. Google seems to expose itself as the people whom I don’t want to be tracked by by engaging in shady behavior. That is exactly the problem.
Yes, anyone who wants to can circumvent it anyway, but that doesn’t stop us from judging those who do so negatively†. Google can be held accountable in this case (by, for example, complaining loudly about what they do) and there is nothing wrong with doing so. Just because it’s possible doesn’t mean it’s right.
That the protocol sucks is in that context a separate and unrelated issue. It may be security theater, but that doesn’t make Google’s behavior any more moral†.
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† Insert clever analogy here. I’m too lazy to think about one, though.
So if tomorrow Chrome uploads all your keystrokes to Google, will that be a valid defense?
>P3P means "we would never..." in computer speech which is unenforceable therefore useless.
Stopping Chrome from uploading your bank passwords with today's update is unenforceable as well and hence thereby useless.