That's besides the point. It's still a massive intrusion of privacy.
It's like a stranger looking over your shoulder, and you can't even tell it to bounce.
I wonder, if police wanted to search your phone, can they unlock with your fingerprint against your will?
No, in the UK they can't just take your finger and press it to your phone or point it at your face to unlock it. They can service you a notice demanding access to your phone, and not providing access is a crime.
In most countries they can. Which is why you should (in a perfect world) have password or fingerprint unlock, and if you use the fingerprint, the phone wipes itself. Not even Graphene supports this.
Wouldn't that lead you to getting charged for destruction of evidence?
Only if you told the police to unlock the phone with your fingerprint. If they did it without your involvement, it's allowed.
Yes, but wouldn't the fact that you intentionally set the phone up to wipe itself be enough to charge you for that? You've pretty much made a booby trap for the police.