Instinct is part of the self-preservation process of being human. Instinctively people view others different from themselves with suspicion. But over time with interactions they learn behaviors to get along. The behaviors can be "good" or "bad" from society's perspective depending upon how the interactions turned out for the participants.
Political Correctness (PC) is taught (either directly in school or the rhetoric of social and political leaders) rather than learned by personal interaction. Under PC, one is taught to suppress one's instincts and embrace certain groups and ideas deemed worthy of special deference by social and political leaders . . . and shun those groups and ideas deemed unworthy.
PC's suppression of the self-preservation instinct inherently makes us more vulnerable to those among the "worthy" groups who would do us harm . . . and less likely to affiliate with the "unworthy" groups with whom we may have common interests.
Simply, PC is a method of "divide and conquer" . . . . and we are being divided today by the politicians in Washington like never before.
Race, gender, sexual-orientation, affluency, political affiliation have all become the subject of strident rhetoric to divide us into squabbling groups . . . while the distraction allows groups who would do us harm escape notice while attending to their nefarious tasks.
The entertaining Brigitte Gabriel hits the nail on the head when she explains the harm of PC in the clip below:
In a nutshell, evil can exist and take root in ANY group. . . . The Germans, Japanese, Russians, Chinese are all called out as having spawned evil at one time or another. (I would add the Italians as well -- I'm sure you can think of others). PC was not an issue before, and evil among these groups was recognized, confronted and dealt with.
Evil needs to be confronted wherever it is. Today it is the Muslims where evil is taking root. Brigitte reminds us that treating this group differently due to PC from the way we dealt with the others in the past threatens our existence.