So we're all connected in this world. how can people treat others like dirt?

we're all humans in situations that are more fortunate than others. and at the end of the day we're all connected. imagine if every single person was a brain cell sending little electrons to each other to grow.now imagine if there were some brain cells just denying any more info and bein rude and cynical.everyone should let any thoughts and info flow no matter how stupid it may seem. SO WHY DENY anyone?why should there be groups or whatever? nobody really has a clue anyway