#### in one hand and put your opinions in the other.
Either way you'll have #### in both hands.
Personally, I think they're right, Mustangs and Jag-stangs and Jaguars and cyclones and all that are mid-range guitars, no matter how you look at them. That being said, a little elbow grease can make these unique beauties shine and make some wonderful tones (providing you don't alter the #### out of them)
As an aside, those guys are right to call it a "childs guitar" because it's the sort of guitar a child would have a wonderful time learning on, since it's a little smaller and the action is so good it's amazing. The great thing is, a lot of people started learning on one, and then decided "this beats a strat any day, #### upgrading, this is my guitar!"
I guess what I'm saying is, if you're used to playing a strat/tele, the mustang can come across as a bit cheesy, but if you know what you're doing, it'll be fine.
EDIT: Plus, those guys are old and elitist, so therefore, their musical influences are all boring and old school, they don't know how good a mustang is for playing punk!