I would think the answer would be obvious too O, but i guess it's not for some people.
Maybe the people who know it already just want to see how long this will go on? or just feel too embarrassed to say anything since no one has caught it yet.
But the most basic and simplest answer is the golden rule. Dont do something to others you dont want done to you. Everyone is supposed to learn this very early as a little kid. Emotions about losing someone shouldnt make you not want to kill, but because it's just plain obvious when you think about it.
It's like John Locke's state of nature. Reason tells you the golden rule. But of course there are some who dont listen to reason, and do things because they really want to, or they think they can get away with it, or something like that. Most likely because they havent learned to be reasonable very well. Which seems to be the case almost everywhere in modern society.
On the idea mentioned before, that nature gives us consciousness. That's a very interesting thought. Since humans or our lower species were becoming so smart and learning how to use tools and make fire and all, it would be just natural that we would develop consciousness to understand what we are doing, and reason, and make morals for ourselves.
Hopefully in that idea, once we get to some stage we will develop some higher level of consciousness to understand what we're doing and realize we're destroying our places to live and all that good stuff. Just hope it doesnt come too late.