As a simple example: it breaks ad networks, which rely on you having a cookie that is shared across many domains to figure out what ads to show you. That doesn't really work if that 3rd party script is blockd.
The industry's dirty little secret is that for all the hand wringing about tracking and targeting, the tech is still really in its infancy and doesn't work very well.
Network ads already don't pay very much (IMHO) and removing the ability to build profiles on demographics would make them worth much less.
You're right that it's not a dealbreaker -- my startup would be OK since we ads direct to clients -- but mostly people aren't in a position to do that. It takes a team of ad sales and support staff, and a very particular kind of niche content.
I'm not sure what the problem is - all they need is to ask the publisher to set the cookie for them. Then it's a first party cookie that is relayed on the back end to the ad network, who gets all the same information from it that they used to get.
Here's what it managed to get from my iPhone 6[1]. This would be the same 'fingerprint' as virtually every iPhone 6 user in the UK.
This is a very effective response by publishers because many users who would have enabled 'No Ads' simply will not bother to enable 'Do Not Track'
You (and the ad networks) seem to be under the mistaken impression that you have some sort of a right to that information. You don't, and acting like a stalker should be treated as such.
As another poster said, you target your ads to the content it is being published next to. Seriously, can you not see the damage you're doing by pushing "surveillance as a business" model? If your hopefully-profitable idea relies on a key aspect basically every single dystopian story ever told (fiction and non-fiction), maybe that's a sign you should find another way?
The alternative, if you want to keep pushing stupid gimmicks like that "coupon" thing, it will just push more and more people into treating the advertising industry (and later, internet commerce in general) as the enemy.
That sounds awesome.