There is absolutely no benefit to Down Syndrome.

I know a guy who has down syndrome and he is the happiest guy I've ever met. Any time I see him, even if he doesn't see me, he is smiling and just looks like he loves life. When he sees me, or anybody else he knows, he gets the biggest grin on his face. When you talk to him, you can tell he is such a happy guy with no stress.

If that is not a benefit then I'm not sure what is.

There is absolutely no benefit to being many things that some humans are.

Surveys consistently indicate that people with DS, their family members, and people who know them consider their lives better because of it.

That's a benefit.