It’s crucial to have a balance between the three branches of government, and between the states and the federal government. Each branch of government should have some power to serve as a check on the others.
The federal judiciary consists of the district courts, which are the trial courts, the courts of appeals (circuit courts), and the Supreme Court.
It strikes me as odd that a district court judge should be able to stay or overturn a presidential policy or a state law. That seems to contradict the idea of a “balance” of powers. It would be analous, perhaps, to a county (at the state level) or an administrative agency (at the federal level) having some power over the Supreme Court.
It’s even worse when you consider that sometimes such a ruling comes from a single judge — not even a panel of judges.