> If I send you a letter and you promptly burn it, that does not entitle the police to imprison either of us

Aside: The fact that someone (legally) deleted data or (legally) switched to an encrypted channel may still be used against them, when establishing mens rea regarding some other actual crime.

That said, I don't want to dissuade anyone from taking steps to be safe.

I think that only establishes mens rea if it's not part of your normal procedure. If I always shred my mail that has my information on it after reading it, then shredding a piece of mail allegedly related to some crime is just normal. I would have to be an unusual intentional act, such as only shredding the illegal mail and not the regular mail.