I don't think I have any ethical obligation to Facebook whatsoever. My browser is my agent, not theirs. I can and do already modify lots of sites to hide cruft (like "social recommendations") I don't want to see; do you think I have an ethical obligation to consume a site exactly as its creator intended it to look? Do I only have an ethical obligation if the creator stands to somehow make money from it? What if what I'm blocking isn't an ad but is a referral link where they'd get paid if I go there and buy something?

There is no coherent position which creates an ethical obligation to view sites in full and unmodified (especially given that one of the primary purposes of web browsers, historically, has been to mangle what a site sent to you into something that's actually a sensible and renderable document tree).