Another major reason that the spec was abandoned was that no one could agree on what "tracking" meant, and so what "respecting DNT" would even mean.

I leave it enabled out of the principle, and as a data point. Every person who has such a feature enabled is sending a message: we do not want to be tracked. It's a blip in the dark, but you can't stop the signal.

I'm much happier with the GDPR idea where tracking is not allowed by default and the website has to obtain informed consent first. Of course in practice the implementations still need to be improved - both through enforcement (many of the consent dialogs are not legal), through additional standards and legislation to require them (you should be able to set your browser to automatically deny all requests) and through continuing to shame companies and individuals for their excessive tracking (at least the consent dialogs tell you about the extend now).

I think if you'd ask most people if they want to be tracked they'd say no. Of course you could word things differently or promise benefits to manipulate the answers, but just for "do you want to be tracked" the answer will typicall be NO - and some more progressive privacy laws like the GDPR recognize that by making no tracking the default.

Setting DNT to true by default is certainly more in line with user's wishes than the previous assumption by the tech industry to just grab whatever info they can.