That dissolves the meaning of the word. A quick look at the thesaurus links "sacred" with "consecrated, cherished, set aside for an elevated purpose, guarded, inviolable." Antonyms include "irreverent, secular, profane, degraded, unconsecrated."
Human nakedness is strongly laden with meanings: on the one hand, privacy, intimate knowing, trust. The mother nursing her baby, the lover and the beloved, the joys of the marriage bed.
On the other hand, without the privacy and the intimacy, nakedness is linked to depersonalization, shame, degradation. Date rape, the brothel, the slave auction, Auschwitz.
Do you think a man would see his mother's, wife's, or daughter's nakedness plastered up on a billboard as "consecrated, guarded, inviolable"? Permit me to say I doubt it.
Well, I suppose you could eventually get to the point where none of it means anything. No height, no depth, no heaven. Hell? Yes, if after you get past the heat, hell ends in cold.
There is a good one for you. Many Americans think a mother nursing her baby in public is completely inappropriate for the same reason they object to breasts on billboards. Germans consider it natural, and to object is obscene because you are seen as interfering with one of the most basic, wholesome, natural acts. To object to the billboard, you are a prude who can't appreciate the fine form of the human body (or, for the religious, appreciate God's finest creation).