Deciding what happens with all the money? If the government runs finances, they get to say who’s poor and who’s rich. If they get too comfortable with this, they could punish people financially for not supporting them, making all the people who don’t like them silent and all those who do like them crazy about them. People can never be trusted with absolute power, because corrupt people always find themselves at the top of these systems. Hitler, Stalin, Zedong, Mussolini, etc. Like Captain America said in Civil War, “things are run by people with agendas, and agendas change.”
A few years ago, Democrats tried to control who had guns. (They would later abandon this pursuit to rail on the police to get people mad at Republicans, but it’s still government control).