I agree with everything you said, but as a practical matter I wanted to point out that it is possible on Facebook to like something and then "hide" it from your newsfeed. This allows you to register your like without all the spam. This is what I did with "Barack Obama", because I do support him and wanted to publically acknowledge that, but I don't need to see three captioned photos of him per day.
That doesn't stop your likes resulting in targetted advertising to your contacts (depending on their how-closely-they-follow-you settings, presumably).
For instance I sometimes see "sponsored links" of the form
"<sister-in-law's-name> likes <retail-outlet>, here is an offer that they have on at the moment" - I've never liked <retail-outlet> on facebook let along done that and subscribed to see absolutely all posts from them.
Yeah you're probably right about that. I think they can each individually hide those though, right? In any case, I agree that the UI for this is terrible and that's probably by design to make it less likely that the masses will hide everything.