Humans are cruel animals, very cruel.
On one hand, we have people, capable people, that botched they luck throw in life and due to it were pushed (well, technically they were pushed by us) into comitting crime (say, stole food because they were hungry) when all they needed was just a bit of help from us, more fortunate humans. And what we do to them? We throw them with murderers and rapists to facilities which, few countires aside, do exactly the opposite of what they were created for. They push people that were not quite sure yet into full criminality. We literally destroy their chances at "normal, decent" lives for one mistake which was made under pressure and bad luck and we say they deserve this.
On the other hand, we have people, very unfortunate people, that completely botched their luck throw on birth with critical failure (I'm not particulary talking about the kid from the article, just in general, people beyond help). Due to this they have pretty much no chance for "normal, decent" live unless they roll critical success on life luck throw, though chances for that are rather miserable. Hell, some of them don't even know what is happening around them. And we put them before life of hardship and pain with zero-to-none chance to overcome this and load of self-loathing on the chance they'll actually realize how much trouble and pain they give to people around who take care of them. And in this situation, where it's more merciful to put the bullet in their head instead of making them go through this, we "help" them saying "Hey, look at the bright side, at least you're breathing" like just breathing was the best thing ever (and don't get me even started on people who were unfortunate enough to survive accidents with heavy injuries like say, full body paralyzation where they can effectively only breath). Sure, it's not their fault, but life isn't fair.
And you all hypocrites, ask yourself and answer honsetly. Just how many times did you say or think something along the lines "I'm going to kill you"? No, it wasn't different, it's exactly the same. And putting those thoughts onto paper instead of keeping them to yourself doesn't make her more of monster, or you less. Granted, she should handle it better. Much more effective and constructive way would be to go to the parent and say something like "If you won't stop this child from wailing in xxx seconds, I'm going to kick it until it stops wailing and preferably moving.". Or even cut the middle man and go straight to the kicking. But yeah, I'm pretty much on the side of the woman. Though I might be a little biased since all I need is a kid, any kid, no retardation needed, entering my field of vision or just hearing them to make me want to acquaint their faces with the pavement.
Inb4 "Well, you... prick! I guess it would be more merciful to put the bullet in your head?" - yes, it would be. That'd be nice.