you NEVER kill a dog in a movie. NEVER.
...because American moviegoers are a big, fat, dumb bunch of infants who can't possibly handle the earth-shattering complexities of a CANINE death...!
I quote Wikipedia:
The film received a certain amount of backlash regarding the 'mutant' dog, in particular, the scene where Martin mercifully euthanizes the dog, which is hideously deformed and kept in a large observation room. Many viewers were disturbed by the dog's appearance and sad fate as mentioned by Chris Walas in the documentary for the Special Edition DVD. He said the audience would feel more sympathy for a mutated animal than a human.
Michael Bay even made his views clear on the subject during the "Armageddon" DVD Commentary. YOU. DON'T. KILL. THE. DOG!! I mean, people just can't handle it!