I will be among the first to decry the awful trend of treating dogs as fashion accessories - i.e., Paris Hilton handbag dogs; dogs need to be allowed to be dogs, they need the freedom to run, play and enjoy life canine-style. However, there are indeed legitimate instances when a dog needs to be carried or otherwise transported not under his own steam.
Elderly dogs, handicapped dogs need the socialization and mental stimulation that comes with getting out and about - it would be unfair to deny them this in their twilight years. A carrying pack or stroller often adds greatly to the dog's quality of life.
Also, very small dogs are sometimes at risk of being crushed in crowds as they can't be seen - hence a pack for those situations.
For the OP: these threads might be helpful to you:
Pet carrier recommendations Hiking with my old dog - Need some ideas.
But for all hale and healthy dogs - nothing like a good workout to keep a dog happy and fit.
Actually, the BVet has a campaign running: 'Bewegung, Bitte!'
http://www.bvet.admin.ch/tsp/03157/index.html?lang=de