NYC has one of the strictest laws in the world but that never stopped criminals. Israel has gun control but if one lives in an area or considered dangerous, is/was a reserve office in the IDF and has a clean record one can get a permit fairly easily yet the murder rate is very low, especially when factoring out terrorism, underworld hits and “family honor” killings.
America has a huge population so statistically there will be more people who go nuts. Also the mentality regarding violence is very important.