We Mormons have a unique perspective regarding our mortal bodies, and that comes from the Mormon doctrine that our Heavenly Father has a body of flesh and bones.
Tangible, but not mortal, God is not a personage of spirit, but a glorified, exalted, celestial Man with a resurrected and glorified body in which His eternal spirit dwells.
Because He loves us and has a plan for our eternal happiness, our Father in Heaven sent us, His spirit children, to earth to obtain mortal bodies through which we would be tried and tested to see if we will keep His commandments. Eventually we will all die--our spirit separating from our body for a while--but because of Christ's atonement and resurrection, all mankind will eventually be resurrected as well, the spirit and body to never again separate. Those who choose to follow God's plan and keep His commandments will not just rise from the dead with resurrected bodies, but with glorified, exalted and celestial bodies.
Even though these mortal dwellings of our spirits are imperfect and corruptible, the bodies we've been blessed with house our spirits and are God's sacred creation. Wise and grateful Mormons respect their bodies as gifts from God. Our body is the instrument of our spirit, and our challenge here is to make our body the best we can, and to use it as wisely and obediently as possible.
The wise and righteous use of our body includes how we display it for the rest of the world to see. Clothing that is too short, too tight, and too revealing in any way mocks the sacredness of the body and affronts our God. Tattoos, body piercings, and even too many piercings in the ears both disfigure and call inappropriate attention to a sacred gift. Photos of ourselves or our children that are placed where all the world can see them should accurately reflect the respect and esteem we have for our bodies, by being modest and promoting the sacred joy we have in these bodies.
It is not that Mormons are not grateful for our bodies, nor is it that we do not think them beautiful gifts from a divine Father. Modesty itself is a public statement as to just how grateful we are for the precious gift of our physical bodies. How we treat our bodies is a reflection of just how grateful we truly are.