Humanity simply doesn’t have a brain capable of it.
People can only mentally relate to a certain number of people or ideals. Anything else becomes foreign. Our animal brains see foreign things as potential threats, and puts up guards. Suddenly, a person starts to wonder: why don’t those other people do it the way we do? The ‘it’ here can be anything: Religion, politics, pick any subject. That question evolves into a disagreement, then an argument, then a schism, and so on.
Within a population where that is happening, there will be a lunatic fringe. This fringe will take that idealism to the extreme, and as power shifts through time, eventually will have their turn at the wheel. In power, those former disagreements will turn into demands, for rectification or subjugation. Eventually, it will become war. This war can be within the power structure of an online forum, up to clashing nations. It’s inevitable.
Is there an existing evolutionary pressure to push our species away from this tendency? If not, and I don’t believe there is, we will continue to fight amongst ourselves forever in one aspect or another.
As demonstration, disagree with this assessment. Consider your amount of zeal, and realize it varies among people. How might they react, given enough impetus? To disagree by yelling or striking out, through social, legal, or physical means. Even just one with enough power in social or legal contexts could exact revenge. Or perhaps someone else gains enough followers to shout this article down, or have it banned.
Driven far enough, someone will eventually make it personal and direct their attention to the author. The author and their supporters will become the new enemy. Again, various attacks would be used to force the article down, or have adherents socially abused, arrested, or ultimately killed.
Writ large, we see this happen every single day even within otherwise genial groups. Our inability to recognize it within ourselves is our downfall. It becomes Democrats versus Republicans. It becomes Pro Choice versus Right to Life. It becomes Free Speech versus Social Justice. It becomes “us” versus “them”.
We are simply too primitive to do otherwise.
Humanity simply isn’t wired for peace and understanding. We’re too easily frightened, too subjective, too aggressive. Too many base, animal instincts we can’t consistently override.
The world will continue to remain turbulent, and anyone who says otherwise is full of lies.