SPAM is unsolicited email sent on your dollar, consuming your resources.
At least when I receive spam, I know the spammer has no idea who I am or whether or not I opened their message. Website advertisers try hard to track everything, even when you are very clearly trying to stop them; that is what DNT has demonstrated.
Ads are implicitly requested when you visit an ad-supported site
No, the page is what is requested. My browser is not obligated to do anything at all with the webpage your server sends it. There is no implicit request; you explicitly asked my browser to request ads from the advertisers you choose to do business with.
People making a big deal about this should perhaps rethink why they are entitled to someone else's work (the website) without respecting their terms (the ads).
You put your work on the open web. You did not put it behind a paywall. You did not force me to view your ads before seeing your page.
Nobody wrote an ad blocker because they were angry about textual ads or banner ads. Ad blockers exists because the advertisers have no respect for anyone's desire to not be tracked, to not have hover ads, pop-ups, pop-unders, Flash, Java, and other adware annoyances. Advertisers have shot themselves in the foot with their own greed, and if your website is not saying, "No, I do not want you to piss off my users with these antics" then your website is part of the problem.