Assume everyone in a population governed by direct democracy is not "dumb." Then, there is still a need for checks against what political scientist Alexis de Tocqueville called the "tyranny of the majority."
From the United States National Endowment of the Humanities [0]: "In America, [Tocqueville] saw and praised a people who enjoyed an unprecedented equality of conditions and political and civil liberty without endangering order or prosperity. But he also saw and criticized the way white majorities supported the institution of slavery and the unjust treatment of free blacks and Native Americans. In fact, the greatest danger Americans faced was inherent in their treatment of unpopular minorities."
"The power of the democratic majority arises from the fact that every individual is assumed to be competent to guide his own life and is politically the equal of every other individual. In this situation, the greatest legitimate power will always be with the majority."
A lack of "intermediary institutions, [makes a country have] “no lasting obstacles” in the way of the opinions, prejudices, interests, and momentary passions of the majority and tends towards an unthinking despotism over unpopular minorities."
[0] https://edsitement.neh.gov/closer-readings/alexis-de-tocquev...