The mob doesn't elect our government. Individuals go into a booth and pull the lever. In a fair election, their is no interaction between people when the vote is cast. Sure, there are campaigns and such, but the voting moment is one person at a time inside their head. Mobs become a thing unto themselves and group into a dangerous thing. Their are numerous studies about how people act differently as part of a mob.
Ok yes this is the true meaning of mob referring to in-person groups. But 'mob' in this discussion was being used with respect to groups of people in a more general sense like people on the internet whom all act individually from their own houses.
replying to a group conversation (reddit thread, hackernews comments, twitter chain, etc) is closer to a mob than an individual activity.
The purpose of voting is to deflect responsibility for failures of governance to the governed. After all, they're the ones who put those people in charge, so they're responsible. It's also to take away much of the historic reasoning for revolutions. Who is being overthrown when it is the people who elect the government? The fun trick with representative democracy has been the weaponization of psychology to control the possible outcomes of the public electing their leaders.