I'd like to take this opportunity to demonstrate how groupthink is a vicious cycle. Even if the majority of Slashdot were to agree that Facebook is a privacy nightmare (and let's face it, they probably do), people still resort to blowing each individual small problem out of proportion to try and support their hypothesis. We have a case of what is essentially fundamentalism - finding facts to fit the theory instead of finding a theory to fit the facts.
In this particular instance, have you considered that 'liking' objects is left up to the discretion of the user? It's not a case of "everything I view on the Internet will be visible to my friends and relatives". Previously, if I had found a product that I liked but didn't know who in my social circle could find a use for such a thing, then there would have been no feedback from me, as a trusted friend/relative of the searcher, for the searcher to rely on in deciding which brand of the product to buy. Now there is.
Don't want it seen? Don't like it.