On Fundamentalism

"People who refuse or preach against diplomacy are hiding selfish intentions" is a thesis I tend to lean on, but it puts me at odds with so many in this age that has yet to understand confirmation bias en masse while at the same time we find ourselves pushed into echo chamber thinking due to the ego artifact of the human condition, reinforced by social media algorythms. How strong is this thesis? Am I right about people having a blind spot to group problem solving, or am I deluded by my own bias?