Under dictatorships, you will be found guilty if you are found with an SD card full of encrypted files.
While the encryption does protect your data, it definitely doesn't protect you. Probably hurts you, as people will start applying iron bars to find out how to uneceypt your data.
Dictatorships don't need proof to beat, detain or kill you though.
Having an encrypted SD card is bad, but so is looking suspicious, knowing someone suspicious, having the wrong shaped skull etc etc etc.
As I said, I pray that I never have to live in such a society.
Hidden volumes or steganography have been around for a while for the explicit purpose of 'plausible deniability': https://www.truecrypt.org