Here's the problem.
Depression is something everyone can agree is a bad thing. It affects anyone's life negatively.
But to a short guy who's overcome the insecurities and moved past them, he doesn't see being short as a bad thing even though a lot of other people do. And he wants a romantic partner that doesn't see it as a bad thing, either.
He wants to believe his partner doesn't give a second thought to his height. Because he's been told for his entire life that he's less attractive, less powerful, less masculine because of this factor, and he's seen a large percentage of women go for the taller guy for his entire life.
But now he's in a relationship with someone that he considers above that, a girl who is part of the smaller percentage of women who don't care about height.
He's categorised her as one of the
good
ones. On his team.
What she said though, has turned his entire world on it's head. Suddenly, it's not him and her against the world, she's part of that world that thinks being short is a bad thing. Something you wouldn't wish upon your children.
You believe that she's just thinking of the children. But the problem with that is she's choosing to agree with the others that being short is a bad thing. It's giving in to that toxic mentality.
Try to look at it as some other people in this thread put it.
Think about if it was interracial marriage in the 1960s, and a white woman told her black husband they should just get a white sperm donor so that the children wouldn't have to deal with racism. It's giving into that toxic mentality and basically saying "who you are is less important than appeasing the assholes who think this shit matters".
It doesn't even matter whether she's saying "I don't want short kids" or "I don't want our kids to deal with this". Either way that's acknowledging her own belief that short men
are
inferior.
And finally, women in this thread just don't seem to realise the significance of telling a man his genes won't be passed on. For many men, the idea that your lineage is continuing isn't just about the social influence you had upon your child, but about the idea that it's a genetic descendant of yourself. There's a reason some people want to have their own kids and not adopt.
Even if she had the best intentions, telling a man you don't want his genes is really the ultimate worst thing you can say to him. Ever.