The courts find the Bill of Rights just too much trouble. Radley Balko gives examples at the link, and concludes:
. . . So if you’re a cop who wants to search a home without a warrant, simply knock on the door, claim to have heard “rustling around” or to have smelled marijuana. Break in and search the home. If you find something illegal, make your arrests and celebrate your success. Just remember to note what you smelled or heard on your report, and be sure to note that you originally knocked on the door after mistaking it for a different one.
If you don’t find anything illegal, you’re probably going to be fine. It’s expensive and time-consuming for an innocent person to file a civil rights lawsuit over an illegal search. Most won’t find an attorney willing to take the case. Most won’t bother to try. For the few who do, your qualified immunitywill make it difficult for them to even get in front of a jury. Again, remember the courts aren’t likely to second-guess your claims about what you heard or smelled, even if your search comes up empty. On the off-chance that your victim somehow gets over those hurdles and gets to trial, you can take comfort in the fact that juries rarely rule against police officers. Finally, if you somehow lose in front of a jury (what bad luck you have!), unless the search resulted in bodily injury, your victim isn’t likely to collect much in the way of damages. And unless you’ve done something really egregious, the city or state that employs you will likely indemnify you. The taxpayers will foot the bill. That’s usually the case with your legal representation, too.
Point is, there’s plenty of incentive for you to bend or break the rules. Busts, seizures and arrests are good for your career. Depending on what you find, frequent searches based on little more than hunches will help you know which hunches to trust, making you a better cop. On the other side, there’s almost no incentive to play it by the book. Take the time to get a warrant and the perps get time to move the drugs. You’ll probably do dozens of illegal searches before someone complains, and once that happens, there’s plenty of machinery in place to both protect you from liability and to prevent the victim from collecting.
This isn’t to say that all cops want to conduct illegal searches.* Only that the courts have provided a pretty easy-to-follow road map for those who do. But that’s sort of the point. Those are precisely the authorities from whom the Fourth Amendment is supposed to protect us.
(*Though let’s be honest, finding ways around the Fourth Amendment certainly makes the job a bit easier. And if the courts have made illegal searches this easy, and mostly consequence-free, at some point you have to question what illegal really means in the first place.)