Your employer MUST make this deduction. Perhaps it was to provide charitable assistance to the elderly poor. Charity must not have been the reason for such a pervasive tax. Perhaps the Social Security system was meant to compel people to save adequately for their retirement. However, Social Security has nothing to do with savings.
Money is taken from the workers and paid directly to the elderly.
The transfer program merely dampens the economy by diverting funds away from real investment. The tax, then, does not seem to have been imposed to solve problems of savings, either. The most likely explanation for the passage of the Social Security Act is that the country was in the midst the Great Depression, unemployment was high, and pushing the elderly workers out of the labor market made room for others to get jobs. Perhaps the Social Security tax was also imposed merely to bring the United States closer to the socialist ideals of the communists in vogue at the time. Social Security, then, was never a good idea.