>Under normal circumstances, the president wouldn't be shooting the country in the foot, so I completely agree that in this instance, perhaps it is good that a district judge can do this. But if American politics starts getting played this way, I think you may see significantly more challenges in getting good laws passed. I am not saying this is a good law.
Except it's not "getting" played this way. It's been this way for a long, long time.
What you're missing is that Federal district and appeals courts are not the final say. They can make (and do so all the time -- and have done so without issue for a very long time) rulings that are in conflict with rulings from other Federal courts.
The Supreme court is charged with addressing such conflicts.
The way this has worked is that judges issue rulings and those rulings are often "stayed" (not put into effect) to allow for appeal. However, when significant harm is being done prior to such appeals playing out, judges will not stay those rulings.
That can create conflict between the 94 Federal court districts when a court in one district rules one way in a case and a court in another district rules another way in a similar case.
And the way that's resolved is that those cases are appealed to the Supreme court which removes the conflict.
The problem with today's ruling is that it empowers bad actors to ignore rulings from some inferior jurisdictions and operate with impunity in other inferior jurisdictions.
More tellingly, the ruling specifically limits inferior court rulings to the specific parties to a case. As such, if the government acts unlawfully, only those who have actively filed suit against the government are covered by such rulings -- even if the actions taken by the government are blatantly illegal and/or the government's actions will likely be deemed inappropriate on appeal.
Which opens a loophole allowing the government to circumvent the courts (which are a co-equal branch of government and not meant to be subservient to the other branches) by blatantly breaking the law (e.g., stripping a natural born and/or naturalized citizens of their rights as citizens and shipping them off to god knows where without due process) against those who have not filed suit (either because they don't have the resources to do so and/or are deprived of the opportunity to do so by the executive branch).
And as long as losing party (in this case the executive branch) doesn't appeal (either to appeals courts and/or the Supreme Court) their loss(es) in inferior court(s), the Supreme Court never has the opportunity to address the conflicts (if any, as this is still a loophole even if no other courts have ruled on similar cases), essentially giving the Executive branch carte blanche to do whatever they want to anyone who hasn't pre-emptively filed suit and/or anyone they illegally (i.e., without due process) hold incommunicado, whether in the US or on foreign soil.
I'm not sure how things work in your country (as you didn't say which one it was), but I'm guessing that you wouldn't appreciate being disappeared without recourse if the government unilaterally decides to do so.
The issue isn't whether a single Federal judge can make rulings affecting the nation, but rather that the Executive and Legislative Branches must heed the rulings of the Judicial Branch, regardless of where those rulings originate.
If the other branches don't like it, they can appeal (and the Executive Branch doesn't even have to wait for such cases to reach the Supreme Court via the appeals process, they can go directly to the Supreme Court and ask them for a ruling immediately) such rulings.
This decision stands that on its head, effectively saying that if you are not a named plaintiff in any Federal court case, any ruling doesn't apply to you unless and until the Supreme court rules on the case one way or another.
Which, as I mentioned, allows the Executive Branch to avoid judicial scrutiny by not appealing rulings against them.
In the past, the Executive Branch would need to get appeals courts and, eventually, the Supreme Court to rule, removing ambiguity and conflicts (if any), this ruling creates a fractured and ambiguous legal landscape where relief from government overreach only applies to those with the ability and resources to sue in Federal court.
This is not fixing something that's broken, it's creating a multi-tiered justice system that the Executive Branch can manipulate to do pretty much anything it wants, even if it's blatantly (like stripping natural born citizens of their citizenship -- cf. the Fourteenth Amendment[0] to our constitution) illegal.
[0] https://en.wikipedia.org/wiki/Fourteenth_Amendment_to_the_Un... [1]
[1] Section 1 of the 14th amendment reads: "All persons born or naturalized in the United States, and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside." [2]
[2] To clarify, since you're not from/in the US, Amendments to our constitution, once ratified (by 2/3 majorities in both houses of congress and by the legislatures of 3/4 of the several states -- the 14th was ratified in 1868, so this is nothing new), are incorporated into our constitution -- which is the supreme law of the land in the US.