Why can't we live in peace together and celebrate each other holidays, such as Christmas, Hanukkah, etc?

My neighborhood back in NYC was Jewish and Catholic. We celebrated religious holidays except for church services together. It used to be great. Actually we attended each others funerals and weddings also. This was back in the thirties, during and after the depression. I still get almost uncontrollable urges for kosher foods. everybody sharing their desserts etc.it was fun I miss those days. Most people are against that now. Part of their distaste is because of the weirdos handing out poisoned foods and other types of trouble makers.