They can snatch a few people, but what if everyone starts doing that?

Well designed steganography would not be easy to detect if the authorities don't know what they are looking for. Do they just beat random people to find out if they are sending hidden messages?

Okay you caught the person, so what?

XCGHJ DFVBN TYGBJ

With OTP, it could either be

KILL THE EMPEROR

or it could be

Bring the Condom (something that's embarassing and plausible to want to hide, but not overthrowing the government)

or it could be any 15 character value, just think of any plausible thing you could possibly hide, to downplay what the real message is.