And typically this is assumed to be in a superiority form of way as a default, because we associate it with the way we all collectively tend to talk about objects.

That assumption seems loaded: relative value is unstated.

The infected must maintain a safe distance or remain quarantined to prevent further infection.

is highly impersonal & could refer to any organism. However, it doesn’t inherently disrespect or dehumanize. It’s a factual & neutral statement (or implied instruction) that focuses on a specific quality.

Saying it directly to someone would be weird unless they’re announcing it to an entire room (depersonalizing). Still, it’s not suggesting anyone is lesser than human or necessarily disrespecting them. Common notices work the same way.

We don’t need people constantly reminding us we’re human to understand they’re not denying our humanity.

if the person is so socially naive that they genuinely don’t understand this and it’s a honest mistake

Or they disagree with your take. Others share your take, but it’s also a commonly rejected take. It’s not a logically necessary take.

If, however, you become informed of how this comes across

As if the informant has authority on the language for everyone?

Everyone is entitled to their opinion. That includes opinions that oppose unreasonable & unjust opinions.

Unless acting abusively, expressions that merely disagree don’t necessarily make someone an asshole. Deciding it does looks more like going on an expedition for assholes that aren’t there.

This distracts from the question, though, of whether such depersonalized language goes further & necessarily dehumanizes. I think there’s fair disagreement that it does.