Why is it hard to say 'no' in Turkey?

Campaigning has begun in Turkey for a referendum in April on changing the constitution.

The reforms would boost the powers of President Erdogan. In the run-up, those pushing for a ‘no vote’, against the change, are finding some problems getting their message across.

The BBC's Mark Lowen has found that in today’s Turkey, you can say everything but the word 'no’.