"Slander" entails making false statements, whereas this was just a statement of fact, free even of condemnation. People who read it make their own value judgments.
I read the statement and to me, the future progressive seemed to be the most apt way to phrase it. When I tried to find examples to illustrate why, it occurred to me that the future progressive predominates when delivering bad news. For example:
"Unfortunately, we won't be renewing our contract with you"
or
"We regret to inform you that we will be going with another candidate"
Changing those to the simple future makes them sound much harsher to my ears, so I would venture that the progressive is a mechanism for softening the impact.
This sort of construction is reminiscent of topic-prominent languages, e.g. Japanese, but English is a subject-prominent language and phrasing it that way would sound awkward to a native speaker.
I apologise for the generalisation. That was too broadly and absolutely worded. But I would stand by the idea that "people on the spectrum are more likely to have difficulty intuitively learning social conventions".
> No wonder people leaning towards the Asperger/autistic spectrum of brutal honesty would state that; such is their nature.
Actually, it is not "their nature". The nature of people on the spectrum is to have difficulty understanding social conventions. Having a system whereby social conventions are explicitly spelled out in detail is likely to help people on the spectrum adhere to them, because they no longer have to be inferred.
People on the spectrum deserve understanding (like everyone else) when they break social norms or say hurtful things due to not understanding that they're doing anything wrong. When they know that what they're doing is not acceptable, they are as responsible as anyone else who knowingly acts like a jerk.
I'm also highly skeptical of the idea anyone outside of a tiny minority would be unaware that "garbage" is an intentionally insulting term, especially given that it is a metaphor. Even "completely fails to meet standards" is vastly better and more descriptive (outside of the emotional content of "garbage").