You're not painting over the billboard, just blocking the light reflected off it for yourself. It does not affect others.
What if you only block your competator's ads? What if you replace them with your own? (..does Brave do this?)
What if you block all ads (yours, and your competitors), but in so doing, exploit the inertia of a consumer who is a.) already using your product, and b.) actively sheltered from exposure to the market?
ohh, i got it: just don't block ads for FAANG /s
Ad blockers having paying partnerships can be a problem, but something like Ublock Origin does not.
It also keeps a handy "cost to advertisers" metric you can view. I'm over $40,000 at this point.
Why is it morally wrong to paint over billboards?
But even if we accept that unfounded premise, the equivalent of ad blocking would be to hold something in front your eyes blocking the billboard as an ad blocker does not prevent other visitors from seeing the ads but paint does.
There are two ways of thinking about what a webpage is:
1) A web page is a billboard
2) A web page is a pamphlet
If a webpage is a billboard, then it is morally wrong for me to paint over those sections of the billboard that I do not like (i.e., using an ad-blocker). This viewpoint is held by those who own webpages (because they want control over it) and by those who cannot change what a webpage looks like (common users).
If a webpage is a pamphlet, then I'm free to cut it up and re-arrange it however I want. Naturally, those with knowledge to cut and re-arrange are more likely to take this view. This viewpoint is more technically correct, a webpage is just a few bits of information handed to me, and to the extent I control my own computer I can cut up those bits and view them however I want.
It's fair to say that Amazon.com contains Amazon's webpage, and that Amazon owns that web page. And yet, I've never once viewed Amazon.com without using an electronic device owned by myself or another non-Amazon entity. Amazon.com doesn't exist on a billboard, it requires the use of electronic devices owned by other people. What rights do the owners of those electronic devices have? Any?