The short answer is that if it’s acceptable to ignore the law for a good reason, it makes it easier to ignore the law for a bad reason. A slightly longer answer is that law is based on precedent, and any precedent set by such a law could and would be used by our enemies. They already routinely pass unconstitutional legislation to suppress us that gets shot down by the USSC because it is unconstitutional. What happens when constitutionality is no longer an issue?
Last, and far from least, there is a very ugly word used when what is lawful depends on the whims of those charged to uphold it. I would rather see the states secede than live under such a government.
How do you see SCOTUS protecting your rights if Clarence Thomas or Antonin Scalia is disabled by heart attack or stroke, Obozo appoints Eric Holder and Mitchy McConnell and the usual gang of "Republican" $$$$$ obsessives decide that POTUS gets to have his nominees confirmed. How many GOP quisling senators voted against Sotomayor and Kagan and Ginzberg for SCOTUS. Bad habits die hard.