Why do certain conservatives accuse liberals of suppressing others' freedom of speech?

I've seen several conservatives here accuse liberals of suppressing others' freedom of speech. (They especially like to cite "political correctness" as an example.) However, we're not the ones who are trying to get Harry Potter books banned from public school libraries or trying to get Darwin's theory discredited or shunted aside in the public schools, despite the fact that practically all of the scientific community (with the exception of a few kooks) bases its umptions and work on it.