Fourth Amendment law has a complex and tortuous history, and many liberals believe the Burger and Rehnquist courts have dangerously weakened Fourth Amendment protections. But if one basic judicial construction of the Fourth Amendment has survived all the political buffeting, it is the rule that unless police have a warrant, or specially defined exigencies are proved, they cannot enter a person's home even if they have probable cause to believe there is evidence of a crime at this particular time and place. (The proposed public-housing sweeps do not even meet the probable-cause criterion.) Breach that wall and it will be hard to resist legal arguments for military-style sweeps of homes on all sorts of government-contrived pretexts, or for highly selective sweeps that seem aimed at minorities.
Nor is this concern for unintended consequences limited to judicial precedent. However crazy, the "three strikes" laws are probably not unconstitutional under current Supreme Court doctrine. But in our complex system of separated and partly overlapping governmental powers, legislatures have a bad habit of creating messes that someone else has to clean up. As they demonstrate their toughness, they bamboozle the public into believing these measures can be had without tax increases or without bankruptcy-threatening costs on cities and counties that have to foot most of the bill for overlogged criminal-justice calendars.