It can take an entire generation (or two) for an idea to die.
Some ideas weren’t always “bad ideas”. Many times the beliefs related to how an idea came into being and was adopted by the masses were once valid. Fearing people from other tribes who looked different and had different cultures from your own tribe was probably quite literally the difference between life and death. But once we evolved to the point of greeting each other with handshakes instead of rocks and sharp sticks, the idea of “all people who are different are bad” also begins to evolve.
Belief in the now-considered-not-so-good-idea doesn’t immediately go away, but it slowly evolves. Some forward-thinking tribe members start believing it’s a better idea to unite with those outsider tribes for safety and commerce and their new idea now begins to spread. The older generation raised from birth to believe the value of the old idea begin to die (probably because they are being eaten by saber-tooth tigers who are avoiding the larger groups of individual and feeding on these smaller and weaker tribes) and the old now-considered-bad-idea dies with them. A new generation is born believing strangers can be friends instead of enemies.
People once believed the idea that the earth was flat (current outliers notwithstanding). No matter the amount of new ideas (and lands and cultures) being discovered, guardians of the old ideas and beliefs could not be swayed.
However, the end does come eventually and a generation (or two) passes with no one able to recall ever having even met a person who actually believed the idea that the earth was flat.
But as generations evolve, so do the concepts and ideas imagined by those generations of people. What was once literal can become metaphorical. The idea of the earth being physically flat can be reimagined as a way to illustrate a global economy with a level playing field.
History not only repeats itself — or “rhymes” as Mark Twain is believed to have said — it also reincarnates ideas. And the ideas which are reincarnated have nothing whatsoever to do with whether or not an idea is a good one or a bad one. Times and places are just sometimes ripe to revisit a concept in the minds of humanity. If only as a check on our own evolution.
Fear of people who are different is (unfortunately) an idea that has lived too many lives. We (the human race) just can’t seem to get it right each time it comes around, so it keeps coming ’round. The death of this particular idea also seems to accompany the violent deaths of too many others. One could argue that this idea never actually dies completely, but there are definitely times when the world bans together to defeat this way of thinking rather than reinforcing and fostering these thoughts that will lead to our extinction.
Fear is a terrible way to live your life (or to elect a leader). We need wisdom and understanding, not guns and walls. My hope is that the idea of “all tribes that are different than ours is bad” is one that dies out (again) before my own generation does.