What "need to do" could possibly be more important than your baby?
Look, in all seriousness, if you really read the blog post objectively you will see that the baby is in no real danger. She's not letting the baby cry for hours on end - it's a few minutes. And she does, in fact, get up in the middle of the night to feed her. It may not be the way you choose to parent your children, but that doesn't make it wrong.
We, as parents, are all just doing the very best job we can, and for you all to so harshly criticize this woman is unfair and unkind. How would you feel if your sister-in-law decided that you were doing it wrong and decided to rant about it on facebook? And then (to add insult to injury) it went viral and strangers on the internet were all talking about what a terrible mother you are?
And don't try to say that you don't care what a bunch of strangers think, because you do. We all do. As much as we don't want to admit it, we all have moments of doubt. The one thing we want more than anything in the whole world is for our kids to grow up safe and healthy and happy. That means that we all secretly share the fear that we're doing something to screw that up.