I think that's entirely fair: Websites should not track users who do not want to be tracked, but websites should decide whether or not to serve clients which aren't to be tracked.

Well, ideally yes, but let's be honest here. If we can't trust websites to not abuse data, how can we possibly trust them to respect a polite request not to gather the data in the first place? I would personally rather have an incognito mode feature that I have confidence performs the task it claims to do without alerting the website, than one that loudly announces its presence, on the hope that it might be respected.

I don't trust Google, but I certainly don't want Google to trust random websites on my behalf.