While this is true, I can't help but to feel that the Hacker News crowd tends of see only one side of this issue.
They are not asking smartphone companies to introduce backdoors in their products. They are just trying to make sure that police has the right resources to be able to solve investigations.
To be honest, this sounds reasonable to some extent. When someone gets questioned by the police, you expect the person to tell the truth. If the police gets a hint that your smartphone might have significant evidence of some sort of crime, isn't it reasonable to comply with the request?
It's not like they are asking to access it remotely from anywhere at anytime.