While burning the American flag is offensive to many, it is not illegal. Instead, it is considered protected speech under the First Amendment.
The Supreme Court determined that laws prohibiting flag burning are unconstitutional in the famous 1989 case Texas v. Johnson.
The case involved a protestor who was arrested after burning an American flag outside of a political event in Dallas.
The Houston Chronicle recently featured an interview with the attorney, now a Georgetown law professor, who represented the protester and challenged the Texas law that banned mistreating a flag in a way that "seriously offended" witnesses.
Ultimately, the Court held that "the government can't punish people for expressing their opinions simply because the government, or even a majority of Americans, find their opinions offensive," the professor explained to the Chronicle.
However, it is constitutional for the government to ban flag burning when it leads to the incitement of violence, safety hazards or environmental harm. In other words, there has to be another valid reason to prohibit flag burning, other than to prevent people from expressing their views.
The professor said the decision was very controversial, especially because it was issued right before Independence Day. Since then, it has become one of the most important decisions in First Amendment law and it has been upheld several times, by both conservative-leaning and liberal-leaning members of the Court.
In fact, a federal ban on flag burning was ruled unconstitutional a year after Texas v. Johnson was decided. Congress has tried to overrule the decision with a constitutional amendment, and came close, but it was not successful.
The professor acknowledged that flag burning is something that deeply offends many Americans, but he told the Chronicle that it is "extremely dangerous to give the government the power to single out forms of expression and penalize them by throwing people in jail."