It's not quite the same. The government could (conceivably) dictate the content of the code, but the argument then goes that signing the code conveys the messag

It's not quite the same. The government could (conceivably) dictate the content of the code, but the argument then goes that signing the code conveys the message that Apple has 'approved' of the code, similar to signing your name on a particular declaration. Conversely should the first amendment not protect Apple from having to cryptographically sign their code, then arguably the government should also be able to force a person to cryptographically sign a message that runs contrary to their views. Which seems a pretty clear violation of the freedom of speech.