Not sure where you're coming from here, but this 1-sentence comment sounds like something a serial killer would say.
If someone murders your dog, no big deal to you? And sure, this dog was YOUR dog, but you would probably still agree that, in general, dogs shouldn't be killed, right? I'm not saying this line of thinking extends to all living organisms, but surely you can acknowledge there's SOME gray area between bacteria and "organism as smart as a human".
Another useful thought experiment: what would aliens who are way smarter than us think of us? Mightn't they think of us as so dumb that our lives don't matter to them? How would you try to convince them otherwise?
Do you associate with many serial killers, so as to be familiar with what they say? Note that I'm not saying that killing animals is right, I'm asking why it's wrong. This is not a positive statement about the world.
It seems like you think this is very obvious, so why is it so hard to explain why? Shouldn't obvious things be easy to explain?
If someone murders your dog, no big deal to you? And sure, this dog was YOUR dog, but you would probably still agree that, in general, dogs shouldn't be killed, right? I'm not saying this line of thinking extends to all living organisms, but surely you can acknowledge there's SOME gray area between bacteria and "organism as smart as a human".
Another useful thought experiment: what would aliens who are way smarter than us think of us? Mightn't they think of us as so dumb that our lives don't matter to them? How would you try to convince them otherwise?