You may also still wonder why ANY heresy is deserving of death. I would concede that the death penalty is not the appropriate response. But also consider the stakes: Hus was a strict pacifist. He said that anyone practicing war went straight to Hell (and to explain how it was that so many Christians went straight to Hell despite their faith, recall his implication that no-one who receives only what had been bread was saved). The immediate prompt of this radical pacifism was a military skirmish between a pope and an antipope, but this was taught at a time when the Ottoman empire was rampaging across Christian lands; the Byzantine Empire was in utter collapse and the papacy was attempting to marshall troops for the defense of the Christendom.
Ironically, despite Hus’ pacifism, the Hussites eventually killed each other off. During the Battle of Lipany, more than 13,000 Hussites were killed... by other Hussites. The surviving faction submitted to the authority of the Bohemian king, and were allowed to practice their religion in peace.
In 1430, the Catholic Church agreed to permit reception of both bread and wine at mass, providing it was proclaimed that either was sufficient. Many abandoned Hussitism, but it was revived 50 years later when a subsequent pope determined that impanation was still thriving. Following the reformation, Hussites tended to take sides with either the Reformation or the Catholic Church and Hussitism eventually went extinct.