It seems that the Do Not Track feature will only give you a false sense of safety and privacy. It depends on the advertising companies actually respecting your choice, which most do not, according to this article:
Without even needing to read it, it is, you're right. It becomes a bit of an ethical problem at this point where in order to get accreditation, adtech companies need to respect the header but, unfortunately, no one is forcing Advertisers or Publishers to work with an accreditated adtech company.
Also, another problem there is giving 'bad actors' another signal to identify a particular client, as I imagine not many people have the DNT feature enabled currently.