If guns were taken off the street, it would be much easier for people to defend themselves against attackers. Without the advantages of lethal force at the mere pull of a trigger, potential criminals would have a much harder time taking items by force from other people or attacking others senselessly.
Naturally, the crime rate would be begin to shrink in the United States if guns were disallowed. By merely subtracting gun related crimes alone, there would be fewer crimes. The crime rate would go down even further once the crimes in which guns were used as a form of force or persuasion, such as robberies or muggings.
If guns were disallowed in the United States, law abiding citizens would not have them but criminals still would. That means more crime. Also, many existing gun owners would just hide their weapons and not turn them in or destroy them, so that would mean more crime too just because of a gun ban
Crime would not decrease if guns were banned because criminals will always find a way around the law. Hard drugs like meth and cocaine are illegal, yet the use of these illegal substance continues to rise. Many big cities with tough gun laws have the most gun-related crime of the entire country, while cities and states with lax or open-carry laws seem to have the least amount of crime overall. It seems that when average citizens are allowed to carry protection, would-be criminals have to think twice before committing a crime. In cities where having a gun in public is illegal, criminals only have to worry about how long it would take for the police to arrive; in some heavily populated areas, they have plenty of time to do their dirty work and get out.