Burning a flag is already illegal
http://www.wnd.com/2006/05/35976/
A Tucson man arrested last month after burning a Mexican flag in protest plans to burn another one this weekend during public Cinco de Mayo festivities.
Read more at http://www.wnd.com/2006/05/35976/#zWkaAWoXKreSpxtP.99
It even was illegal in Ca when I was a kid 50 years ago.