1)"Of course it's possible to have untrammelled freedom of speech. It may have downsides in many cases, but perhaps that is a price worth paying."
No, totally false. There's a considerable amount of information that you cannot publish. Both information managed by the state, and information that is private to individuals and organizations.
There's a considerable amount of information that many individuals would like to publish that definitely does not constitute 'whistle blowing'.
It's not a 'straw man argument' because the issue is relevant every day to journalists trying to make this decision.
There's considerable consternation among even major/professional media outlets about what parts of leaks they can publish, what they can't, moreover, there are entities (i.e. bloggers) who'd just publish whatever, whenever, without considering the consequences if they didn't have to.
So sorry, you can't publish pictures of your naked girlfriend, or private medical records of employees, or many state secrets.
2) Manning published gigabytes of data for which he had no knowledge of the contents - this is not 'whistle blowing', moreover, his publication of the video journalists dying in a war zone does not fit this description either.
Nobody has the right to enter into a firefight in the most dangerous location in the world, and to not inform the combatants (as per protocol) and expect that they will be treated with the normal rules of application of violence in a civilian area.
Of course, were the journalists were to have informed the US forces of their intentions, they would have been told to 'absolutely not enter because your safety will be ensured'.
The video shows the folly of individuals who think they can just walk into a war zone with cameras. There was no crime.
3) "Finally, why should free speech protections be restricted to journalists?"
Well, first consider that 'shield laws' as they exist generally only apply to journalists, so take that up with the government, but it hints at my point which is that the 'rules are vague'.
Your understanding of 'freedom of speech' as conveyed by your comment seems to be flawed: nobody ever had the right to publish 'whatever' under the guise of 'freedom of speech'.
Summary:
- There is information that cannot be published, there is no debate here.
- The rules at to what can be published is unclear.
- The 'shield laws' are vague, and especially the terms of what constitutes 'journalist' is vague, further complicating things.
So if we want the journalists to be able to 'do their jobs' we may need better, clearer regulation.