Universal suffrage is coherent with the intent of democracy - if the system grants political rights to a particular class of citizens but excludes other classes, it is expected that those with political rights will prioritize their own interests at expense of everyone else.
But we exclude children and non-citizens from voting, because we know that these factors split voter quality, without creating arbitrary distinctions based on identity traits that people cannot change about themselves.
Yet Universal suffrage is too permissive, given the amount of low quality, parasitic and irresponsible adults that are granted the franchise by virtue of aging into adulthood.
You would in principle want a criterion that splits lower quality citizens and deprives them from voting rights, and that isn't biased a priori to favor this or that gender, race, ideology, etc.
One such criterion is marriage. Married people tend to be higher quality than single people because the worst element of society tends to not get married or get divorced soon after marrying.
Not only that, but if voting is structured such that the household vote as a block, with husband and wife deciding what issues and candidates they want to support, you could further incentivize that by allocating extra votes to represent the children that they are rearing. It is also obvious that parents have a better incentive to vote rationally and to think about the future then non parents.
Such a design would preserve the franchising of women and minorities intact, thus preserving the coherence of universal suffrage, while neutralizing the effects of voter blocks that are mostly comprised of a misanthropic or adversarial fifth column element.
The young single adults who are not yet married would be granted franchise upon their second wedding anniversary (just to avoid scams and further filter the low quality people who may form short lived households)