Personally I think this is because of too much individualism. However, I'm no expert on such things. I just feel this intuitively. I also have no perscriptions on how to change it. It's just the way things are now.
Discussion
What you call individualism is the result of collectivism. Collectivist-altruist philosophy and tribalism is what leads to people who can't think or properly defend their positions. A lack of individualism is the problem.
An individual necessarily must think and use reason in this world. A collectivist follows a tribe and uses violence or fallacies because he has nothing else to offer.