It's the casual part that is inappropriate. The government should not casually threaten the citizens.

You keep using the word casual here, but what exactly do you mean by that?

The statement seemed anything but casual. It has likely been worked on and vetted by multiple people, and while it does have a somewhat breve and light tone, I don't think that qualifies for 'casualness'. For a statement meant for a broad audience, the tone seems appropriate enough.

It's a blog post. It has a breve and light tone. There aren't many ways to make it more casual. Perhaps a tweet?

Legal threats shouldn't be made this way, especially by a government toward citizens.

Most people don’t understand how regulatory agencies actually operate (banditry), but most people do vote. So they have conflicting goals; on the one side, they need to create a paper record so that judges will approve their future banditry, but on the other side they need to disguise their intentions from the public. This blog post by the FTC is unusually well done and effectively meets both goals, so I disagree with you that the threats shouldn’t be made this way as it is clearly in their own benefit to do so.

I find your post deeply ironic because I have found a number of AI proponents to be the source of casual threats to their co-citizens ala "We're going to use AI to automate you out of a job. Better learn to adapt by paying us to use our tools yourself. If you can't hack it, sucks to suck, lol".

One company was encouraging people with a contest to take some guys work to train models and see who could best replicate it. They sent an email to the guy to let him know and say how unfortunate it was he was their target but offered to work with him to train an "official" model.

Casually threatening is how I'd describe those interactions, not this FTC post. Not suggesting that you approve either by the way.