> Extending human-like moral weight to even non-human mammals is a rare idea
It's actually pretty frequent to demonstrate deep empathy and give more importance to pets that to unrelated humans. Some also argue that humans can be morally inferior to others. Drawing a line between human and non-humans may be tempting but the opinons down there are very diverse. Just a few years back and a common agreement would be "Extending white-like moral weight to even non-white..."
> most vegans don't care about the insects killed in farming
Of course they do! But found out it's the compromise with the lowest externalities. Most meat eater also don't like slaughterhouses but think it's a necessity.
> Extending it to literally alien bugs [...] is an incredibly niche idea
I bet if humanity do encounter alien bugs, this idea will be way more discussed. Moral is often somewhat put aside when engaging a fiction: Starship Troopers or Happy Tree Friends are perfect exemple. Most would's joke about that if that was real.