Censorship never takes away the Right of Free Speech, as the Right is immutable. Rights cannot be "limited" by some external authority; they can either be exercised or not, but that's contingent upon an individual making that decision. The freedom to express a Right might be restricted by an authority, but the burden of proof of why this should be rests with those who wish to do the restricting, and that needs to be done on a case by case basis, not in the form of wide legislative action. Freedoms can be restricted, Rights cannot, but Freedoms should only be restricted if such exercise would impact the Rights of another.
Should parents "censor" media from children? Absolutely, if they see fit to do so. This should be done under a parent's concern for children, not exposing them to the harsh realities of life before they can comprehend them. This isn't censorship at all, only safeguarding a child's innocence, and is reflective of good parenting.
Should "snuff films" be censored? Of course. Actually, they should never be made -- those making such a film are clearly violating the victim's Right to live and should be punished for doing so.
Should child pornography be censored? Of course as well, since it can be assumed the child's Right to be a child has been violated by an adult, and again, as in the case of snuff films, the law should fall like a ton of bricks on those creating such media.
Pictures from the Holocaust? Not at all. Although disturbing, showing them impacts no one's Rights -- you can choose to look or not. Moreover, these represent historical experiences that should be analysed in the context of the culture they came from. By doing so, hopefully we will see that we have evolved.
Confederate Flags? No again. If you choose to fly one, I can choose not to look at it. Again, no one's Rights are impacted. Does it stand for slavery? Does it stand for the Second American Revolution? In a free and tolerant culture, these issues should be publicly debated, and so the artifact can be seen for what it was.