Margaret Somerville Puts It In a Nutshell

... Political correctness excludes politically incorrect values from the "all values are equal" stable. It shuts down non-politically correct people’s freedom of speech. Anyone who challenges the politically correct stance is, thereby, labelled as intolerant, a bigot or hatemonger. The substance of arguments is not addressed; rather people labelled as politically incorrect are attacked as being intolerant and hateful simply for making those arguments.

It is important to understand the strategy employed: speaking against abortion or same-sex marriage is not characterised as speech; rather, it is characterised as a sexist act or a discriminatory act against homosexuals, respectively, and, therefore, as, in itself, a breach of human rights or even a hate crime. Consequently, it is argued that protections of freedom of speech do not apply.

Another part of the same strategy is to reduce discourse to two possible positions. One must be either pro-choice on abortion and for respect for women and their rights, or pro-life and against respect for women and their rights. The possibility of being pro-women and their rights and pro-life is eliminated. The same approach is taken to same-sex marriage: One is against discrimination on the basis of sexual orientation and for same-sex marriage, or against same-sex marriage and for such discrimination. The option of being against such discrimination and against same-sex marriage, as I am, is eliminated. That is not accidental; it is central to the strategy that has been successful in Canada that resulted in having same-sex marriage legalised and maintaining the complete void with respect to having any law governing abortion.

In short, political correctness is being used as a form of fundamentalism, and fundamentalisms, especially "warring" fundamentalisms as manifested in the battles between religious fundamentalists and neo-atheist fundamentalists such as Richard Dawkins, Sam Harris and Christopher Hitchens, are a grave danger to democracy. They vastly widen the divides between us, creating an unbridgeable "us" and "them" when what we need is a "we" ...

Margaret Somerville, "Correctly Squelched" (via FMS)