Chad Perrin said:
The swastika has been used for other purposes for hundreds of years before World War II, including as a Christian symbol, while the hammer and sickle went from obscurity to symbol of an oppressive, mass-murdering regime in a relative blink of an eye.
The hammer and sickle has much wider acceptance. It's still the symbol of Aeroflot, it's a popular design on t-shirts and the like, and variants incorporating the hammer and sickle or other work-related symbols (spade, torch and hoe in the case of the British Labour Party's old symbol) have enjoyed considerable popularity and virtually no controversy. The regime was murderous but the ideals it traded on were not.