For me, it's ethical. Loading trackers/malicious connections/contents on my own machine is unethical. That's it. I don't run those on your server, why do you run them on my devices?
What I said is simple: there's ethical pricinples standing by users' sides, and nothing for websites.
If you think it's unethical, you do you. I won't participate in arguing about your personal preferences.
Loading malicious content certainly is unethical. I'm not disputing that, I run an ad-blocker and I advocate to everyone that they should.
However, that isn't what we're talking about, we're talking about blocking ads as a concept. It is pretty indisputably unethical as it breaks the social contract of the service delivery.
The fact that is easy to do, has no punishment, and is incredibly low stakes doesn't make it ethical.
Problem is, ads now are trackers. Of course, there are few ads that are not. I also won't mind if the ads are static images (that are not generated from/linked to 3rd-party/trackers) and unable to click on. Thing is, those are just rare, and in practice blockers can't block them by default, because they are not distinguishable with other contents. So in general, those are not blocked, and blocking "ads" (the ads that are trackers) is still ethical to me.
And just FYI, blockers have the rule that don't block self-promotions (self-advertisements) by default.
I would dispute that there is such a social contract, any more than there is a social contract that if you download a patch to fix DRM, you are implicitly agreeing to install the virus it comes with.
Ad-funded businesses are engaging in market dumping, subsidizing their offerings by poisoning the minds of billions of people, and creating anxiety, insecurity, and dissatisfaction in the process. If someone gives you something for free covered in lead dust, and you accept it but clean the dust off first before touching it, I don't see the ethical quandary. Particularly when you know their widget cost them a fraction of a penny, and they were being paid to give you the poison.
Like Bill Hicks said, these people are Satan's little helpers. Engaging with Satan and undermining him may be unwise, but it's not unethical.
As others have pointed out, these people also have a level of stalking going on that I don't think the average person (or even a relatively informed person) can grasp, and so there's no possibility for a social contract to exist there.
There is a supermarket that at the checkout has a bowl of candy that operates on the honour system.
If you push a button next to the bowl of candy an ad will play and you can take a piece of candy. The candy itself costs a fraction of a cent to the business and the business doesn't care to put anyone in place to monitor compliance with button pushing.
This system is known by everyone and operating in this way for decades so there is no deception towards the person at the supermarket.
Is it ethical to take a piece of candy without pushing the button?
(Actually, in reality I'd ignore the candy since I don't need more sugar.)
I wouldn't have this opinion if user-hostile web advertising and tracking hadn't driven me to it.