Great idea, let's start with the following holidays/traditions: * 15 shevat * purim * passover * second passover * lag b'omer * shavuot * the three weeks * the 15th of av * rosh hashanah * yom kippur * sukkot * shemini atzeret & simchat torah * chanukah * kapparot Here's [a more complete list](https://en.wikipedia.org/wiki/Jewish_holidays). After that we can give it a century or 10 to determine if any other holidays need to be banned.