Jet-Poop has a point when it comes to the U.S of A, but around most of the world, it's quite obvious who is responsible for censorship. In countries where religion plays a major part in politics, for example, nearly always the religious, right-wing parties (for it mostly goes together) are almost entirley responsible for censorship.

Take Israel, for example. There is no law against advertisements featuring people with exposed shoulders. However, religious people will not step on a bus with such an ad. on it. So they are effectively censoring such adverts. Also movies, etc. I have never heard of any left-wing attempt at censorship in Israel. Admittedly, this is because the right is so extreme, that it pushes the left further left. But that is not the topic here. What matters is that the right is entirly responsible for censorship.

I guess it all depends on the balance of power within the country, and how fanatical the sides are. I'm sure that the left in Israel would be more tolerant in many cases than the left in the States, just because in Israel, freedom of speech is more of a debatable issue, with very strong opposition, and it is less taken for granted.