I have worked with people with Down syndrome in the past, and I must say they are amicable, nice, and with the proper education they can quite compensate for their condition.
That said, I don't know whether they're part of the "intended" human condition. They don't seem to hold any advantage over non-Down people, only disadvantages. If anybody is scared about similar thoughts, consider doing a non-invasive pre-natal test (NIPT) during a pregnancy; it's a test that checks the infant's DNA in mother's blood, and has a great accuracy.
That said, I don't know whether they're part of the "intended" human condition. They don't seem to hold any advantage over non-Down people, only disadvantages. If anybody is scared about similar thoughts, consider doing a non-invasive pre-natal test (NIPT) during a pregnancy; it's a test that checks the infant's DNA in mother's blood, and has a great accuracy.