Bumper stickers are at very best minimally tasteless. But the perfusion of round, bubble lettered, grotesquely-cute-figured bumper stickers proclaiming that "Life is good" fulfill every criterion of tastelessness we know.
While we certainly condone flaunting curvaceous earlobes, flouncy hips, and delicate ankles, we do not condone flaunting privilege. The issue here is similar to the distinction in tastefulness between costume jewelry (eminently tasteful) and gaudy displays of precious gems (horribly tasteless). If you have the strange fortune to live in the most-consuming country in the world and drive an SUV (or wear t-shirts, or do anything really), for golly's sake don't proclaim in stupid bubble letters that "Life is good."