As I understand it, the original intent was to make sure that only people who had shown some relative stability were able to vote. They chose property ownership as the criteria for that.
The opposite side of that coin was that they knew what happened to previous democracies where "The Mob" (the general populace, not the Mafia) was allowed to vote and how easy it was to sway the common populace with personal greed and the emotion of the moment. Which gets back to the desire to only give the vote to people who would - hopefully - show a more long term and responsible point of view.
There really are people who shouldn't be allowed to vote because they are too stupid or too irresponsible. The problem lies in finding a reliable mechanism for determining who those people are.
JMO - I still like the idea of two levels of citizenship. Everyone of natural birth or naturalized citizenship is provided the full protection of law but only those who have shown some willingness to go above and beyond, who have shown some level of personal responsibility, would be allowed to vote and hold office. Given human nature the natural inclination of that is for the enfranchised to pass laws discriminating against the unenfranchised (or recently disenfranchised) so any tinkering with the current citizenship system would have to include hard and fast protections again that.
Bottom line is that a universal franchise is what eventually kills democracies or democratic republics. We have seen that historical fact played out since the 1930's at least.
