I am asking purely from the perspective of logic and consistency.
No, you're not. Because:
Feel free to explain how it is a straw man for an argument on abortion because I cannot see how it is. The specific issue of downs syndrome differs massively from choice or other causal factors for abortion.
Downs can be taken out of this comment and still have it achieve the same goal.
"It is a crime to kill a person because they have Down's Syndrome, how is it not illegal to abort a fetus tested to carry Down's Syndrome markers?"
"It is illegal to kill a person, how is it not illegal to abort a fetus?"
You're simply narrowing the broader question. The broader question is the one you care about. You're looking for a foothold to broach the broader question.