The fact that you indicated you like it and want to share that with your social network has not changed. If you "like" a brand, it has everything to do with brands and advertising. You just indicated that you like that brand. And by doing so you've told Facebook that you want that endorsement to be public. Just the same as if you were to "like" a blog post. You want everyone to know that you like it. Otherwise why would you be publicly announcing it on Facebook?