Your kind of forgetting that Harry has been in Justine’s position, he delivered his child whole and healthy.
His daughter was already born, he never knew about her until she was six years old. Also as a fetus, little Maggie didn't have a Hunger Demon feeding off of Susan till the point of most likely dying giving birth. No, I am not forgetting, Harry was never in Justine or Thomas's position. He did chose to kill the mother to save the child, himself, and his grandfather... Susan agreed.
You have a point, but I still don't know if I'd ever bring it up. If I were in Harry's shoes (I'd be a whimpering pile of neuroses, but that's beside the point), I might ask, "How can I help her through this?" But I cannot imagine jumping right to, "Have you considered aborting it?"
No, that wouldn't or shouldn't be the first words out of Harry's mouth.. On the other hand that conversation never got to take place because with in minutes of that Carlos showed up. I am not sure either if the implications of the danger to Justine or Thomas' fear for her had sunk in yet. Harry's reply was mostly about the trials of becoming a father, what he was going through.
(and of course, no way Harry would bring it up. I mean... seriously. At least over here you don't bring that up, mostly because it's common to only tell people about pregnancies when it's slightly advanced so you've sort of already decided... so bringing it up would be second-guessing, too).
What is odd, if people are right in their calculations that Justine is only six weeks pregnant, most women don't even know at that point. Especially if she is on birth control, supposedly Thomas is "for intents, sterile," two weeks late for your cycle could mean a lot of things. We don't even know if she is regular.. Some women aren't. Yeah, I know she got a test, still, has she been to a doctor yet?