The issue with vertical communities is self-stratification. A horizontal community has a diversity of interests and opinions. A vertical community has only what

The issue with vertical communities is self-stratification. A horizontal community has a diversity of interests and opinions. A vertical community has only what you choose. A horizontal community influences your decision-making to be less specialized, i.e., less descriminatory in who it benefits. Vertical communities don't. Not only are you not going to hear from perspectives different from your own, you don't even have to witness the consequences of your decisions on people different from you. For example, as a childless adult, I might vote against the deployment of speed cameras in school zones and never even notice if the number of kids being hit by cars is going up every year.