You do not need to turn on iCloud backups and you can delete them. I’m not sure if they are securely deleted however, and also don’t know if there are some laws that might require Apple to keep backup copies of data on their servers for a certain amount of time.
Anyway, this thread started with the controversy about Apple refusing to help the government gain physical access to a terror suspect’s phone that was protected by a password and encryption. The Supreme Court case is about whether a cellular service provider (AT&T, Verizon, Sprint, etc) can give data about your location without a court order.
But the issues in the Apple controversy are much broader than just iPhones. It applies to any portable device, like an Android phone or Windows laptop, that requires a password to access. And it just keeps getting more complicated since phones are now using fingerprint readers and facial scanners instead of passcodes. Can the police force you to put your finger on your phone? I think law enforcement is currently of the opinion that they can, not sure if there are court decisions on this. With face recognition, all they would have to do is point the phone at you.
Again, you are not forced to use fingerprints or face scans, you can turn it off in the settings and just use a passcode, but most people will opt for convenience over security.