Person is lazier - it doesn't even maintain the acronym. Perhaps if you'd suggested Malefactor in the Middle it would have been a more convincing argument? In general I don't consider 'monster' to be childish - it's often used to refer to sexual preditors, for example. What we're seeing in this line of discussion is that language is mutable and subjective - and for that reason the author's use of words is a justified as any other.