Democracy exists because voters are too stupid to form their own decisions. It relies on the hope that stupid decisions are largely random, while informed decisions will all tend in the same direction. It takes only a small minority of people to know what they're doing, if the uninformed ones can be counted on to mostly cancel each other out.
That's obviously a fraught assumption, but mass media puts an increasingly large wrinkle in it. It takes only a small thumb on the scale of uninformed votes to overpower a minority of informed voters, and new techniques increasingly enable people with a lot of money to apply that thumb. If only 1% of voters are informed, and a misinformation campaign can sway 2% of otherwise evenly-divided voters, it becomes the dominant factor -- even if the informed voters are unswayed.