Why are Flavius and Marullus upset when the play opens?

Flavius and Murellus are upset because they see the common people parading in the streets instead of working in their shops. They demand to know why the men are not working. A cobbler informs them that the people are celebrating Caesar's victory. Murellus is infuriated by this information, and calls the workers, "you blocks, you stones" (1.1.34). He then tells them that Caesar has not defeated an enemy, but rather that Ceasar has killed the sons of Pompey the Great.