Political correctness is essentially a requirement (developed and enforced by liberals) that the primary objective of any word or phrase (written or spoken), decision or action is not to offend anyone. Ostensibly because offense makes offended individual unhappy (sometimes very unhappy).
The problem is that by requiring and enforcing political correctness, liberals violate probably the most fundamental human right – the freedom of speech. And the secret of happiness is not forcing others to avoid offending you (which is impossible anyway), but conditioning oneself to have no emotional reaction to offensive speech or behavior – and immediately forgiving those who offends you.
Political correctness puts individuals under a severe stress (which sooner or later makes life hellish indeed) and thus makes everybody deeply unhappy. Which means that “liberal medicine” (i.e. political correctness) is far, far worse than the “disease” (i.e. “offensive speech” or “offensive behavior”).