Although the result of working out is perhaps a more attractive body, the health and wellness benefits far out way the superficial ones. Do it to take care of yourself, you owe it to family/future spouses to be preventative rather than have future unnecessary illnesses. The benefits of exercise and proper diet are well proven and written about, not many in this part of the world can deny hearing about them.
edit: I agree with above, it crosses the line to become vanity when it consumes your life or you are obsessed with it. Also if you get into taking unhealthy supplements or steriods (ie bodybuilder etc)