My reasoning is simply that:
- life's too short to continue reading a book I'm not enjoying
- there are already so many good books that I can't read them all and people still keep writing them ;)
- if I haven't read the whole of a book, I don't feel I should review it
I know not everyone feels this way, and I do see the whole professionalism argument, but at the same time, I'm not a reviewer or book blogger by profession.