Hello, I’ll try. (while I was writing I noticed that I was talking more about existentialism in general, not only about the Absurd, hope you don't mind)

First, we have to consider when existentialism started being so strong and popular. It was after WW2. After all of the deaths, pointless suffering, gruesome, horrifying events. I mean… how can you just go on? How can you still think that God loves us, or that hope is a thing, or that with all of this … our lives do truly matter?

When you really start questioning (Do our lives matter? Why are we born? Why do we suffer, why do we die?), you can basically sum it up in one question:

Do things have a reason? (or rather… Is the Universe reasonable, and therefore not absurd?) Now, you might say “yes, there is a reason why things are happening, scientific, religious or of other kinds” but this philosophical system works with the thought that, no, there is not.

The Absurd is, I think, exactly that – it’s when you confront the absurdity, meaninglessness of the Universe, the lack of meaning behind all of this. Behind our lives. And you start to wonder then, why the heck do I live?

And that’s when existentialism really starts to kick in.

Now, you were born, you probably didn’t ask for it, but here you are in this world. You’re a human, you have will and you can make decisions. And decision, oh you will make. You have to, actually, that’s the price you pay for being alive, having will and thinking. But don’t worry, existentialists know how much making decisions can be overwhelming and how it can make people anxious (trying to pick an ice-cream in a shop with thousands of flavours that all look good can be literal hell for some people). (Un)fortunately it also means you have a responsibility for your actions. We are not given our fate, we create it. Thus, we could say, we create our own meaning in the Universe. We just have to note that this meaning 100% personal and not objective.

This could all make us super sad. We could lose ourselves in despair. But … should we?

Heck no! No, we should enjoy life! We should carry our boulder, even though we know it’s utterly pointless and it doesn’t have a reason. And yes, we are going to suffer, quite a lot, actually, but still. Why not make enjoying life our reason to live? Wouldn’t that make sense?

When one confronts the lack of meaning in the Universe, the Absurd, there are many ways they can deal with it. One of them being the approach of existentialism.

(I know that there are probably some mistakes in this text, but I hope it helps.)

>If you think humans aren't privileged in relation to all other life on earth in this context then it's OK to destroy humans for your benefit the same way it's OK to destroy other things for your benefit - since it's all the same, right?

Maybe it's not OK to destroy anything for our benefit? That way - yes, it's all the same.