No, not everything else is extra.<quoted text> "Are we only on this planet to breed?" Yes. That is our job. To continue the species. Just like every other animal. Everything else is extra.
That would make religion extra, which will throw you into an endless loop of circular reasoning.
Medicine is not extra, or all your breeding wouldn't go very far. Everyone would still die by the time they hit 35.
Science is not extra, see reason above.
I could go on and on, but you should get the idea by now. Merely breeding is not all that is required. We also have to build on our existing knowledge base, otherwise people would have to rediscover fire every few years.
Oh, and adoption matters, because parents die and somebody has to raise those kids.
There are a lot of ways to matter. And your opinion of mattering is very different from mine.
Mass murderers can have kids, too. So can rapists. Raise your standards, putz.