Your supposition that consent can morally come from two seperate human beings,

Not what I said.

For example, if a terrible disease that brings pain and very early death is genetically passed on by one person that decides knowingly to have a child, and the child is born with that disease, one could easily make the argument that it was immoral for that individual to have a child, instead of adopting.

... I guess. ¯\_(ツ)_/¯