The thing is: if encryption is illegal and you encrypt your illegal material so law enforcement can't convict you for it, they can still convict you for using encryption.
Which is such a great idea, because proper encryption is undistinguishable from random data: so, if you have a drive, any drive, good luck convincing anyone that it does not contain any encrypted content, and that whatever is in the empty sectors is just garbage. Guilty until proven innocent.
This is not even about deniable encryption (which is apparently a part of the threat model?): this is a nightstick to beat anybody who's inconvenient in any minor way. "Prove to me that your song collection contains no secret message, else you're guilty." There's no way to do that! For anything I could come up with, the universal response "well maybe it's hidden even better" holds.
In other words, introducing "guilty until proven otherwise" introduces witch-trials pretty much by definition: if she floats, she's a witch (so far, so good; yay it works); if she drowns (or dies in notprisonnosirnotatall after years of not confessing nonexistent secrets), she was innocent. Of course, there is absolutely no way this might be abused, and certainly not for personal vengeance.