People want to lynch the mother without even knowing what happened. It takes like what 2 seconds for a child to slip between/over a fence? Sometimes shit simply happens, and unfortunately this shit was very sad.
It's true that sometimes shit simply happens. Someone letting their kid close enough to a fence and unrestrained (i.e. picked up or somethin') and untended enough to slip through isn't something that simply happens, y'ken?
There may be distractions or emergencies or whatnot that explain it, but it was shit that could have been prevented (pretty easily -- if your kid's that small, keep your hands on 'em or in a stroller if you're letting them near anything potentially dangerous) and it's pretty difficult to excuse that, particularly when it ends up like this case did.
Definitely a bit too much vitriol from some folks, though, as per usual. Doesn't have anything in particular to do with the internet, though... people are just kinda' like that. You would have had similar (if less easily accessed) responses if it had been pre-internet and in a newspaper. Some folks just like to feel and/or act outraged...
Should spend some time going over old letters to the editor and whatnot, really. It's almost fascinating how little some things have changed with the advent of the 'net. Easier to get to, but human psychology only changes so much.