Example: "People should be judged by the content of their character, not the color of their skin"

Saying that phrase, went from forbidden, to controversial, to "you're not allowed to disagree," to "you're not allowed to agree" so rapidly.

Someone who actually holds it as a principle has had enemies on all sides at various times. Many of those who find the phrase offensive are not offended because it clashes with their principles, but because it strikes at the status / tribe signal positions they've adopted.