The difference is, the technology can change underneath you.
For example, suppose Comey succeeds in mandating encryption backdoors. Then the backdoor gets compromised and published. You suddenly have an obligation to use an encryption mechanism you know is compromised to transmit things you have an obligation to keep secret. Catch 22.
In theory a court might realize the absurdity of that situation and let you out of one of the obligations, but how do you know which one it will be? Or that they won't still demand that you do both, effectively requiring you to shut down your business until the government changes the law?
For example, suppose Comey succeeds in mandating encryption backdoors. Then the backdoor gets compromised and published. You suddenly have an obligation to use an encryption mechanism you know is compromised to transmit things you have an obligation to keep secret. Catch 22.
In theory a court might realize the absurdity of that situation and let you out of one of the obligations, but how do you know which one it will be? Or that they won't still demand that you do both, effectively requiring you to shut down your business until the government changes the law?