How is the delivery of a baby with a known abnormal condition ethical? (Warning: may be controversial)

*Note: Ethics is a branch of Philosophy which deals with the issue of the GOOD

You know you are going to have a child with down syndrome or any condition that is degrading or abnormal.

Your love and dedication to the infant motivate you to be compassionate, and your happiness is intrinsic because you have a child.

However, you know that you are limited in the experiences you can have with each other and there are many other variables that arise that restrict your interaction.

As you are intentionally limited and restricted, how is having a child that might be suffering (key word: might) ethical? How is it good to have someone in your life become a potential burden on you and possibly society?

I have asked myself many times, but I find it more neurologically binding than rationally or logically. I am merely looking for your outlook on this so I may understand:

Why do people find having an abnormal child (knowingly) is ethical whereas, it is morally wrong to choose death?

Where do we, as humans, come up with the idea that death is wrong? Note, I typed ‘death is wrong’, not morally wrong.

Also, how does the addition of one more person contribute to society, or the world as a whole, if in the end we still go to the same place? Lastly, does this notion make humans more egoistic because we want to see what this person’s potential may be, or less egoistic because we have an intrinsic motivation to see people prosper?