Parents and voters were shocked and alarmed at the horrific actions of teens and gangs. They demanded a solution and politicians were all too happy to comply. What followed was a wake of bad laws including curfews, school uniforms, and senseless drug testing. Curfews are a bad idea that have been around for quite a while.
Most areas still have unenforced curfew laws sitting around on the books.
Even if they are not enforced, simply having the laws on the books is dangerous. Curfews have historically been enforced against minorities or whichever group has found disfavor with law enforcement officials. During World War II, Japanese-Americans were forced into internment camps or placed under strict curfews. Though the court system initially allowed this, eventually the courts began to show hostility to curfews. The basic idea behind curfews is that young people should not be out and about at a certain time at night.