Dinah's brothers felt grief and anger over Shechem's sin. While it is not a sin to feel these emotions, but the actions Simeon and Levi were evil. They deceived and murdered the men (guilty and innocent) of the city in the name of justice and pride. Then the stole, enslaved, and destroyed what remained, creating more injustice and suffering. The brothers had no remorse.
Decades later, Jacob reprimands them for their actions and makes it known that God does not approve of them.
Righteous anger is real, but we are warned not to pervert justice by making the punishment more than the crime. Vengeance is the Lord's and we are not to repay evil with evil.
Simeon's tribe was scattered and eventually was absorbed into Judah's tribe. The Levites were scattered as well, but they became the spiritual group that blessed the rest of Israel. God can turn sinners around and bring good.