Once Upon A Time In...

Today the first time I'm watching the "US version" of "Once Upon A Time In America" by F Copollo and realize why it wasn't accepted by the US public. There is more than half of movie is so BRUTALLY cut. Aren't we have a mature audience here? In Europe this movie was shown uncut to young adults 16 y.o. or above and none would believe that it would initiate serious society problems. Why shouldn't We understand it right and what is our guilt to be banned from real art?