I suppose if they make using non-backdoored encryption a felony, they can convict them of that, even if they don't know the contents of their communications.

Of course, if there is a back door in all encryption between, say, businesses or minority political groups or anyone else who has legitimate reason to encrypt stuff, 1) there's the chance (very likely) that others will discover the back door, and 2) the government (or some of their employees) will probably abuse it at some point.

See, the whole point of encryption is to make your communications SAFE and eliminate these sorts of unknowns. It's a legitimate need, and just because it can be misused doesn't mean it shouldn't exist.