Replacing ads on the client side is normally associated with the scummiest of malware. I'm not sure how Brave has maintained even a vaguely positive reputation.
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Brave is putting the ads shown (and more importantly reigning in the out of control user tracking and privacy invading bullshit) in the hands of the user.
A side bonus is $ collected and available to content producers and website owners.
If Brave weren't crystal clear about all -- if they marketed themselves as purely an adblocker, for example -- then I think you'd have a point. As it is, it's simply adblocking with a twist.