I agree that sunbathing nude is no more harmful than sunbathing not-nude. If you don't want to use sunblock, at least use sunscreen, and choose your sunscreens wisely. Different formulations filter different wavelengths of ultraviolet light; some wavelengths contribute more to tanning and less to burning and damage, while other wavelengths contribute almost nothing to tanning and tend to be more damaging to the skin.
If you really want the tan, but not the burn, try a UVB sunblock that does not claim to be "broad-spectrum." UVA is responsible for tanning, but also for the premature aging symptoms - wrinkling, uneven pigmentation. UVB is responsible for the cancer-causing sunburns. (This is a simplification, but a decent guideline.)
"Sunscreens chemically absorb UV rays, sunblocks physically deflect them. Sunscreen has long blocked UVB effectively, but until recently provided less UVA protection. New ingredients such as octylcrylene and the benzophenones have improved sunscreen's defenses against shorter UVA rays, and the revolutionary chemical avobenzone (Parsol 1789) works against all UVA wavelengths".
Read the labels!