The thing probably most unrealistic about our headcanons is humans not having massive amounts of mental damage from hearing something saccharine being able to vocalize its pain and suffering in a human language, with the same intonations and motivations as a child. Part of what probably shocks people the most on first contact with the Fluffy Community is that it’s essentially depicting the torture and brutalization of child-coded things.
But who gives a fuck - it’s a fictional playground for those emotions and feelings.
I think the point of the headcanons are to justify things by saying “Yeah, people just lost their empathy” and that’s an (unintended) side-effect of Fluffies being such a persistent problem with no other “solution” besides cruelty.
I don’t know if the lack of consequences would be the only thing that would absolve me of the guilt of killing a Fluffy. I have pigeons landing on my balcony all the time, and despite chasing them away, sometimes they build up enough of a nest to lay an egg. I say a little prayer for it before rolling it off the balcony to its doom; I hate doing it, but at the same time, I can’t reason with the pigeon, and I probably couldn’t reason with a Fluffy. If I let the pigeon nest, there’s real chance of damage to the area, and they come to view it as a “permanent” safe place. This is perhaps why “fluffies as an invasive species” is one of my favorite aspects of the fandom.
I don’t think I could abuse a Fluffy, because it seems like a massive waste of time, resources and clean clothes. I also think I might struggle with begging Fluffies in the city, the same way you struggle with “certain” homeless - if they look threatening or they don’t hit your empathy in the right way, you don’t give a shit. But sometimes, a homeless person (especially with a dog, or a kid) hits that “fuck man, I’m so sorry you had to go through this” and I imagine that nuance with be there when dealing with Fluffies, too.
They still have “sentience” though in the sense they could talk. There’s a reason why the Bugs in Starship Troopers don’t talk, or zombies don’t talk: the burden of humanity is that we have the ability to empathize, and it’s very rare that the things we empathize with have the ability to give feedback so directly. That communication means that we’re kind of obligated to not slaughter them indiscriminately.