"I am one of those who are against death penalty irrespective of who is hanged," former Delhi High Court chief justice judge Rajinder Sachar said.
"There should have been a decency about (today's hanging)," he said. "(Afzal Guru) was not like Kasab (26/11 Mumbai attack convict). He was an Indian."
"The Congress seemed to have made up its mind earlier," he said, adding that his family should have been allowed to see Afzal Guru before his execution.
Suhas Chakma, director of the Asian Centre for Human Rights (ACHR), too urged the Centre to have a rethink on capital punishment, and wondered if Afzal Guru's hanging had made India more secure. "I think the government really ought to consider whether death penalty should continue as a punishment," Chakma said.
"I do not think by hanging Afzal Guru the security of country and people has been enhanced."
Afzal Guru was hanged at the Tihar jail in the national capital on Saturday morning. He was given the death sentence by the Supreme Court in 2004. His hanging was scheduled for 2006 but was stayed after his wife filed a mercy petition.
Ten people were killed in the December 13, 2001 Parliament attack when five heavily-armed Pakistani terrorists drove into the parliament complex and opened fire. Guru was convicted of plotting the terror attack.
Less than three months before his hanging, Kasab, the sole surviving terrorist from among the 10 who attacked Mumbai in November 2008 and left 166 people dead, was hanged November 21 last.
Kasab was the first person to be hanged in India since 2004 when Dhananjoy Chatterjee, convicted of rape and murder of a schoolgirl in Kolkata in March 1990, was hanged in August 2004.
The person to be sent to the gallows earlier than that was Chennai serial killer Auto Shankar. He was hanged in 1995.
The latest two executions in quick succession has rekindled a debate on death penalty. Shailesh Rai, policy adviser, Amnesty International, said: "For eight years not a single execution and in less than three months (two have taken place).
Stating that "it undoes much of the progress" India has made towards moving away from death penalty, he said the global trend was to do away with death penalty. "Two-thirds of the countries are not using death penalty."
Rai said the hanging of Ajmal Kasab and Afzal Guru was "a significant blow to India's progress" to bring an end to death penalty.
Human Rights Watch said: "The hanging of Afzal Guru, following closely behind the hanging of Kasab, shows a very worrying trend by the Indian government.
"Human Rights Watch opposes the death penalty in all circumstances as an inherently irreversible, inhumane punishment," said Meenakshi Ganguly, the South Asia director of Human Rights Watch.