> Between "ethical ad-removal: keeps some ads" and "non-ethical: it removes all of them
You're making up a choice that doesn't exist. No browser presents people with that choice. The choice is: by default you get ads. If they don't upset you, you do nothing. Only if they upset you a lot, you will seek out an ad blocker. Ethical ad blocking means blocking things that significantly degrade the experience of the page or harms the user (such as through privacy violation), while not blocking things that don't harm the user.
So the answer to your question, why WILL people care about ethics - I think they care about not being harmed by slow pages and privacy violation. That is a way of saying they care about other people being ethical to them, and not harming them. A browser that doesn't harm them by default is something they will like. Other browsers will not implement such defaults because there is no standard to support it and the parties who currently make browsers cannot agree on one because they are fundamentally conflicted by their commercial interests.