Why was the Hollywood sign in Los Angeles destroyed in the movie "Argo"? Was the sign also destroyed in real life during 1980?
I assume you are referring to this scene
Was the sign also destroyed in real life during 1980?
It's not destroyed, rather it had fallen in to a state of disrepair.
In 1949, the Hollywood Chamber of Commerce began a contract with the City of Los Angeles Parks Department to repair and rebuild the sign. The contract stipulated that "LAND" be removed to spell "Hollywood" and reflect the district, not the "Hollywoodland" housing development. The Parks Department dictated that all subsequent illumination would be at the Chamber's expense, so the Chamber opted not to replace the lightbulbs. The 1949 effort gave it new life, but the sign's unprotected wood and sheet metal structure continued to deteriorate. By the 1970s, the first O had splintered and broken, resembling a lowercase u, and the third O had fallen down completely, leaving the severely dilapidated sign reading "HuLLYWO D."
In 1978, in large part because of the public campaign to restore the landmark by Hugh Hefner, founder of Playboy magazine, the Chamber set out to replace the severely deteriorated sign with a more permanent structure. Nine donors gave US$27,777.77 each (totaling US$249,999.93) to sponsor replacement letters, made of steel supported by steel columns on a concrete foundation.
The new letters were 45 feet (13.7 m) tall and ranged from 31 to 39 feet (9.4 to 11.9 m) wide. The new version of the sign was unveiled on November 11, 1978, as the culmination of a live CBS television special commemorating the 75th anniversary of Hollywood's incorporation as a city.
In fact, there are comparison shots of the real people and places in the end credits of which the sign is one.
However, if you note the dates above, the sign had been restored in 1978 so, in fact, the movie is NOT accurate as it takes place in 1980.
A little historical licence there...