To borrow a bit of your post Marmalade: "Why is it that we make progress and rightly shun people for cracking the odd "paki" joke, the old shirt-lifters jokes?"
NOT because people kept quiet about them, that's for sure. I love the logic that the best protest we can make is shutting our faces - funny, isn't it, how this "protest" looks a lot like "going along with it".
PP will get more attention on a basic level, because more people will speak about them and visit their website, but they deserve lasting reputational damage from this, and they will get it. For instance, quite a few people I know work in politics, and anything from PP will probably be binned without reading now, rather than listened to.
They've become that guy in the pub who speaks too loudly about how all foreigners are stinking scroungers, and takes the awkward silence that follows as a sign that everyone there agrees with it.