The view of an attractive, young, well dressed men/women can improve productivity - Well, beauty, in all its various forms, is clearly one of the strongest (if not the strongest) driving force for creativity and endless source of inspiration, for men in the first place. Therefore, models clearly are beneficial, since they can inspire people (especially the lonely ones), in turn improving their emotional state and productivity at the same time.
Models are economically active. Models not only earn a lot of money (and thus do not rely on social benefits), but they also pay a lot in taxes, and, what is even more important, they give money to charity as most of the modeling agencies support third world countries.
Models create demand for luxuries. In model industry, there is a lot of abundant luxury, which inspires people to buy luxury goods, that would otherwise lose their appeal.
Indulging in viewing "perfect" men/women may shatter one's ability to live in a real world - The artificial, photoshopped, plastic beauty of models is seldom found in real world. Indulging in it may distract person from the real world, precluding him or her to enjoy the true, natural beauty of real people in a real world. This can cause serious damage to psychical state and consequently day-to-day productivity of (mostly male) individuals, with ensuing detrimental effects on the economy.
Models serve as a deterrent example. All-night partying coupled with bulimia/anorexia presented in media serves as a perfect deterrent for teenagers, who would be otherwise ignorant of possible negative consequences of these excesses.
Modeling focuses almost solely on the visual appearence - Modeling put too much emphasis on person's visual appearence, setting back other parts of one's personality. Many models are therefore just dolls - albeit beautiful ones - naive, with no ideas nor ideals.
Beauty is not a long-term value. Not only that demand for beauty and models creates a consumerist society, but because beauty is a short-term phenomenon, it also fosters a careless/condescending approach towards the elderly, obese...