But you might be partly right. One of the reasons for that are rules of political marketing (rarely politicians have enough courage to ignore them). One of those rules says that you need to differ and polarization is good. You want to win? Show how different you are.
Another rule is that people don't vote with their brains but with emotions. So stirring emotions is needed. Humiliating your opponent is a good recipe for high emotions.
Social platforms are magnifying differences, emotions, so there is no much more left.
As a result democracy is not in the greatest shape now, some would even argue that it resembles more democracy of Roman Empire from triumvirate times (it was only a facade for the mob that was manipulated by those with power) than system that John Stuart Mill or Alexis de Tocqueville had in their minds.