Great first submission, Amber.
Allowing your fur-babies to become obese is simply not kind, and can, as you pointed out, end up being very expensive.
One of the main troubles, to my mind, is that people have little or no real understanding of the needs of a pet.
All our pets have been adoptions, and I was amazed at how many of them did not have a history of vet care!
One extremely old and tubby cat that we adopted because the owners wife hated cats (jerk), had a history of kidney issues, but they had only taken her to the vet once, EVER, and then they couldn't give us the name of the vet she went to.
That same kitty had front and back claws that were so long that they had grown back into her pads and become infected. And yet, they thought they were looking after her in a responsible manner. GRRRRRR.
Naturally, they were "free" feeding her so she got REALLY fat. Imagine how painful her feet must have been and with the additional weight it must have been agony for her to walk.