Like other laws, it doesn't prevent anything. At best, it provides people who are inclined to prevent it a framework which helps avoid getting so bogged down in unending debates about where to draw lines about the boundaries as to never be able to take coordinated action.

At worst it demobilizes action when people get the mistaken idea that the existence of a law is sufficient to guarantee correct behavior without vigilance.

History suggests a poor record of compliance.

That's only with the people who don't uphold the Constitution.

Unfortunately, tyrants—inclulding demagogic ones—rarely uphold laws that interfere with their tyranny.