Probable Cause guards against politically motivated persecution of dissidents
There are so many laws out there prohibiting various things that virtually everybody is a lawbreaker.
If the police are allowed to search anybody they want for any reason they want, then there is nothing to stop them from targeting people for political reasons and throwing them in jail every time.
This kind of selective law-enforcement is already going on in USA. Blacks and other racial minorities are stopped and searched a lot more often than whites. That's why black people doing illegal drugs are much more likely to end up in jail and have a criminal record for the rest of their lives, than white people doing the same thing.
Many US states prohibit people with criminal records from voting in elections. And this kind of selective law-enforcement effectively skews the voting process in favor of whites and against blacks. You could argue with good reason that the cops might be doing this for political reasons.
And of course, this kind of thing can be done against any political dissident, who annoys the government too much for one reason or another.
The Bible says, everybody is a sinner, who needs to be punished by God. And that's the way it is in modern society, with many thousands of laws that make virtually everybody a lawbreaker. Giving the government God-like powers to search everybody and be all-knowing will make life Hell for everybody, except for those who are totally loyal to the government.