I hope that you're trolling, but since that's pretty uncharacteristic on this site, I'll answer you seriously.

Individual privacy, to start. The concept of probable cause to search someone is a concept found in most modern governments. Your communications to other parties privately are none of the government's business. It's an authoritarian measure that assumes guilt without suspicion. As others say, it will often have a racial or cultural component too, and at the very least a class one. People that look and act like the police would tend to be less subject to searches.