I'll state my opinion entirely honestly:
Abortion should be mandatory when it's found that the child is going to have a serious physical and/or mental disability, health problem(s) or will inherit a hereditary disease(s) from one (or both) of the parents.
>inb4 "das oftencive"
I'm probably closer with a disabled person than any of you are. My older brother has severe autism and has poor bodily coordination. He's 26 years old and hasn't graduated High School. He will never become a self sufficient, productive member of society. He will always need other people to take care of him. Medical science was advanced enough at the time of his conception that my parents knew he would be the way he is, yet they went through with the pregnancy. How is it fair to him to subjugate him to live the way he does? And how is it fair to subjugate our family and society to have to take care of someone who will never amount to anything? It isn't fair at all, and not only is it not productive, it's actually counter productive. Parents put a lot of money and effort into children so that they will grow up and do the same, that is, contribute to society and have children of their own, that is how a society sustains itself. But people with severe disabilities, frankly, really don't do that and remain an eternal burden on the people around them, and in the case of a hereditary disease, if they reproduce, create more people with the same problems as them, despite that being avoidable via eugenics. I know this might sound cold at first, but it's true.
>inb4 "wow disowning your brother"
Except I'm not. When my father (only person currently supporting my brother) passes away, no one else in my family will pick up the torch, not even my sister will help. I know this because they've all said it outright. That leaves me, and I will willing do it, despite holding the beliefs I stated above, because at the end of the day he's still my brother and I do love him, but he like many others like him, will continue to be a burden until the end of their lives.
>inb4 "there are people with disabilities who do things with their lives *insert obligatory Stephen Hawkings reference here, even though I'm pretty sure they didn't know he'd have ALS before he was born*"
They are too few and far between. A handful of individual exceptions do not excuse the objective truth about the characteristics, traits and behaviors of a particular demographic.
It should also be mandatory in the case of something like rape (a woman shouldn't be forced to give birth to some degenerate's child, conceived without consent, this is kind of a given) or incest (usually for the same reasons of rape, plus incest = sickly children with severe autism), or that the parents are unfit to raise children (due to a health and/or financial issues).
Other than that, if the parents are capable and the child is going to be healthy and without a severe disability(s), then you're just murdering a person who would have become a contributing member of society and lived a fulfilling life for absolutely no reason other than that you were to stupid to use protection or simply NOT. HAVE. SEX. ("b-but muh animalistic urges!")
Frankly though if you have the mentality that that's OK, i.e., view abortion more as a "Get out of jail free card!" than the last result to an unfortunate case, you should probably be euthanized for being an amoral narcissist anyway.