Just to kinda piggy back off of this, GOMAD has many opponents, including myself, when used with most people. The reality is GOMAD was invented by lifters back in the day when milk was unpasteurized. A gallon of milk today versus a gallon of milk back in the 60's, when raw lifters were drinking six quarts of unpasteurized milk a day and were killing records, are completely different things.
Not considering how unpasteurized milk actually digests (not too good) but looking at the calorie to protein ratio, milk is still kinda shitty when compared to water and whey (as Noema suggested).
The only people that should actually do GOMAD are thin, incredibly active, men who have problems eating the calories required to put on weight. For everybody else, there are cleaner ways to bulk that won't leave your colon a fucking wreck. Milk is great do drink. Building a diet around milk isn't exactly the best idea.
To each their own, however.