Also the ability to disseminate posts to like-minded people creates a sense of false-consensus. Like if you mouth off in a town square the people hearing it and reacting are a fairly representative cross section of the population. If you mouth off on Facebook or Twitter the people reacting are either big enough fans to want to react or sufficiently hostile to what you said that they will lose their shit over it. It makes everything seem more extreme. Your detractors all look stupid, because the most motivated people to pick fights with strangers on the internet are, if we're being honest, more likely to be a little unhinged. Your supporters are also going to be pretty extreme in their agreement and unlikely to take you aside and tell you to chill out for similar reasons.