Let's use the gay pizza incident which conveniently presented both examples:
The pizza owner said he'd refuse to cater gay weddings (because apparently pizza is a huge thing at weddings, but whatever). There were two distinct reactions relevant to this thread:
1)Social backlash calling the business owner a bigot.
2)That one woman who threatened to burn down the business.
One of those reactions will reasonably have to be predicted as the business owner was publicly airing a policy that existed outside of social mores. The other reaction was criminal and therefore need not be tolerated.
Ultimately, the term "political correctness" is nothing more than a repackaging of modern etiquette by people who still want to live by their own obsolete social mores.