You have to realize that people have different opinions on this subject, hence giving you the option to pick either one.
I just feel I would rather not have to shoot a loved one in the face. For me personally, I would probably be going the Michonne way of life. To add on top of my point, she's only a little girl, and it would attract a lot of walkers. It doesn't matter if she still got out, the point is that it's a risk/gamble doing it in the first place.
That last scene with them both was some crazy shit and I was thoroughly compromised of my manhood. Real men cry! :P