In simple terms: When it comes to forcibly removing ideas, it prevents everyone from acting, in order to preserve, in concept, that which they view as worth acting upon. In other words, it assumes that both person A and person B hold views of equal merit, so, because person A's views conflict with those of person B, neither should be allowed to act on his views, or to attempt to manually remove the ideas and practices of the other.
Democracy: Ensuring that no one does anything, all so that we can keep our "opinions," regardless of the sturdiness of their bases.
The contradiction, of course, is that laws are still enacted all the time; the premise behind them rests on the assumption that majority rule is somehow valid -- yet, when it comes to preventing ideas from remaining in the "meme pool" long after they've run their course, a taboo exists, regardless of whether a majority is in favor of their removal.
Note that this taboo exists for all "rights" -- not just the right to freedom of speech. For example, it is permissible in a democratic society to watch sports and get drunk, because those things are part of our "inalienable rights." Causing anyone direct harm as a consequence of those actions, however, impinges on someone else's rights, so we're not allowed to do that. We can, of course, believe that it's okay to harm others in such situations, because that's part of our "right" to freedom of speech. So, then, in a sense, we have too many unjustified "rights," while we also lack good preventative measures against most poor decisions.
Insane, isn't it?