I think that even for site served scripts, there's potential for ad-blockers to do good for your privacy, for example, if Facebook had a script that tracked the movements of your mouse through the page exclusively for advertising purposes and which was independent of the rest of the scripts of the page, then it could be blocked for a privacy gain.
But then, for site served scripts, the provider could sufficiently "tangle" it with the rest of the scripts as to be inseparable, so it's a lost war in the end and your point still stands, I believe.
But then, for site served scripts, the provider could sufficiently "tangle" it with the rest of the scripts as to be inseparable, so it's a lost war in the end and your point still stands, I believe.