Mob rule
Overview
Mob rule, or tyranny of the majority, is a concern in majority rule systems where the majority will act in their own interest at the expense of a minority.
Sometimes the term tyranny is defined as actions that are unreasonably cruel or oppressive. Enacting rules that do not benefit a minority would not by tyranny, all rules and laws do this (or there would be no reason to codify the rule as everyone would already be compliant).
Is it a problem
Maybe, but what is the alternative? All governance systems are created by humans and if rules are not made by the majority they are made by a minority, which is in turn a Concentration of power, whether it be founders, a military junta, or an elite group in society.
The larger the community the less chance selfish groups will be able to control decisions and wider social morality will present itself. Self governance has never been enacted by a large scale community so there is no reference to judge if a large population would be tyrannical against minorities, or more tyrannical than existing systems.
Ways to mitigate
If tyranny is considered 'unreasonably cruel or oppressive' and there is the fear a majority decision could result in this it could be mitigated similar to modern societies, for example having a constitution and constitutional court, perhaps made up by elders or individuals who have proven a strong understanding of the communities goals and rational thinking.
Allowing a community super-majority to for example overturn a decision from the constitutional court could ensure the Concentration of power given to the constitutional court is not abused.