That could also stand as a reasonably accurate description of how karma works on here. It's entirely subjective, why people choose to give/take karma for certain posts. Sometimes, what you say isn't even nearly as important as who you happen to say it to. Aside from having a different name and being publicly viewable, the proposed "like" system wouldn't really be appreciably different than the karma system that's already in place.
Posts made purely to acknowledge another post tend to irritate me. When I see people bump a thread to add little more than "

," I generally just roll my eyes. While it may possibly feed into a certain kind of person's ideas that might somehow makes right - might being measured in amount of public thumbs-up received - I personally don't see any reason to do anything that would make this site any more like Fakebook than it already is - thankfully, very little.