The matching is in itself a violation of privacy, at least if you interpret the right of privacy as "The right to be left alone", as former Supreme Court Justice Louis Brandeis put it.
Your answer is that we should match something other than the user, that happens to correlate with user interests. That is, by definition, not matching ads to viewers.
Viewers get ads matching their interests, as proven by the fact that they are on a related website. I don't see how that isn't "matching ads to viewers"?
> Please don't comment about the voting on comments. It never does any good, and it makes boring reading.
I think you're right in that "site content" is a good-enough proxy for users/viewers/targets for advertising, tho I also readily understand why advertisers would always like more info with which to target their ads.