People tend to forget that there are degrees with Down syndrome just like with anything else. Most of the public face, so to speak, is on the extreme "upper end". In the nineties there was a very popular TV show called "Life Goes On" which was a sitcom about a family with two teenage kids, and the one kid had Down Syndrome and was played by an actual actor (Chris Burke) with Down Syndrome. He, and his character, were extremely "high functioning" and a lot of the time the only way you'd know for sure was the facial appearance and a speech impediment. But not everyone with the condition is mentally on that level, and some don't have good physical health either.
Before you criticize a man, walk a mile in his shoes. That way, when you criticize him, you're a mile away and you have his shoes!
Steve Martin