Not the asshole if by “telling” you mean giving her the advice and then backing off and letting her make her decision.

If you’ve said this to her and she’s decided to move forward with the pregnancy but you’re still trying to change her mind ... then yeah, you are being an asshole. Whatever your feelings are about Down Syndrome, you won’t be this child’s parent. It’s not your choice.

I’m the parent of an intellectually disabled kid. We didn’t know before he was born, and I honestly don’t know what we would have done if we had. As much as we love him, his life is much harder than that of a typical child, and as a parent you don’t want to see your child struggle. But at the same time, I’m not comfortable with the ethics of deciding certain kinds of life aren’t worth living. It’s a difficult decision, and not one you can make for your daughter and her partner.