Ironic since it is the very refusal to reason that makes the phrase problematic. To me, the phrase represents the following argument:
1. I have a strong opinion based on personal taste 2. I realise that there is reason to suspect that this opinion is unfounded 3. I choose not to defend it using argument 4. Instead I will offer a backhanded apology by calling your view “PC”
This is of particular significance to left positions (or activity) because, almost by definition, [reactionary] conservatism is the pig-headed adherence to positions that are no longer tenable and only made presentable through appeal to emotion and use of ridicule (“pc”).
IMHO,
—ravi