Is Zanjeer ka matam - halal or haram?

Zanjeer ka matam was never done even during the days of Abbasid's Caliphate. With the passage of time NEW things are invented which are not the part of Islam. Even many of the Shias don't do this.

Hazrat Hussain (May Allah Karim be pleased with him) is one of the most honored, most respected, and most loved personalities of each and every Muslim who loves the Holy Prophet (May peace and blessings of Allah Karim be upon him). He laid his life for the cause of Islam. The incident of Karbala is the most gruesome and heartrending incident in the history of Islam. The ruthless killing of the family of the beloved Holy Prophet (May peace and blessings of Allah Karim be upon him) at Karbala fills the heart of every Muslim with deep feelings of sorrow, yet mourning the Martyerdom in this way may not be liked by the martyers themselves.

When Socrates was about to drink the bowel of piOSon, some of his disciples and friends could not refrain from crying. He addressed them and said: "Am I dying for some ignoble cause? I am dying for Truth. It is a blessed death. Don't cry."