The former Chief Rabbi, Lord Sacks, has warned of of the potential of social media to inflame wars to global proportions and said: "God himself weeps at the evils being committed in His name."

Speaking in a debate on the freedom of religious belief in the House of Lords, he said that 70 years after the Holocaust, he never imagined the phrase, "Death to the Jews", would be heard again on the streets of France and Germany.

"In all this we recognise the power of the internet and social media to turn any local conflict into a global one. We see how the wilful confusion of religion and politics allows soluble political problems to be turned into insoluble religious ones. We witness the ignorance that allows people to mistake one strand within a faith for the whole of that faith, and we pay a high price for our fascination with extremists. It is the worst, not the best, who know how to capture the attention of a troubled and confused world."

In the past few weeks mobs have assaulted Jews in France, attacking synagogues and setting fire to Jewish-owned shops. There have been attacks in Berlin.

In November 2013, the European Union Agency for Fundamental Rights published a report showing that two-thirds of the Jews in Europe regard anti-Semitism as a significant factor in their lives, three-quarters believe that it has worsened significantly in the past five years, one-third have personally experienced some form of harassment, and they are deeply afraid for the future.

That people in the 21st century are being murdered, terrorised, victimised, intimidated and robbed of their liberties because of the way they worship God is a moral outrage, a political scandal and a desecration of faith itself, Lord Sacks said.

However, opening the "take note" debate, on Article 18 of the Universal Declaration of Human Rights concerning freedom of belief, Lord Alton of Liverpool offered a contrasting view and praised the role of social media in righting wrongs.

He referred to Sudan and the treatment of Meriam Ibrahim, described by the Prime Minister as "barbaric".

The young mother-of-two, who arrived safely in Italy this week and met the Pope, had been was charged and sentenced to death for apostasy and to 100 lashes for adultery.

Lord Alton, a committed Catholic, said: "Having refused to renounce her faith, she was forced to give birth shackled in a prison cell in Khartoum. Happily, given a debate where we will be hearing so much that is so very sad and tragic, international pressure, often led by young internet campaigners, has led to her release."

He said her case was not an isolated one. "Archaic and cruel laws lead to stonings and lashings, with Al-Jazeera reporting that in one recent year, 43,000 women were publicly flogged."

The Conservative peer Baroness Berridge warned: "ISIS has used social media for ill, but we have yet to see religious communities use it to promote their messages. Smartphones have the potential to expose young people to messages like never before and create huge shifts in people's religious affiliations. For that reason, urgent action is needed."

Baroness Lane-Fox of Soho, a cross-bencher, said she valued being able to link on her blog to her short speech without any fear of reprisal. "I can tweet, I can put it on Facebook and, if I am feeling particularly sociable, on Tumblr as well, all of which I can do without fear of any consequence."

Technology was changing the landscape around belief, as around human rights and freedom of expression. "An open internet ensures that people are able to share views, get support and reveal abuses of freedom."

But she also warned of "many risks".

"I asked my wise Twitter followers for examples of where technology had enabled religious freedoms. One story hit home. A young man, who asked to remain anonymous, found me to tell me that he was a gay Christian in Zimbabwe and felt worthless – that was until he got connected. He then found many digital communities all over the world where he could talk about the complex issues that he faced. I was touched that he wanted to tell his story to me in particular because he had seen on the BBC news website that this Chamber had passed the gay marriage legislation."

People find solace and relief in the networks of the online world, she added, the girls snatched by Boko Haram and the story of Meriam Ibrahim spread around the world with a pace and scale that was unimaginable before.

"Just this morning I was reading that journalists are being informed from the depths of Gaza by Twitter. It seems that you can hardly be a self-respecting religious leader without active social media management. The Pope has 4.2 million Twitter followers and the Dalai Lama has 9.4 million. I hope that the most reverend Primate the Archbishop of Canterbury is not dispirited with his 60,000."

Religion takes many forms online. There is a page on Facebook for the Bible, with more than 4.5 million followers. God Wants You to Know is an app that has two million active monthly users. Her favourite was advertisements now being bought around the web encouraging people to "pray for an atheist".

"There are currently 44 countries worldwide that are censoring the internet, and this is immensely serious." The five worst-performing countries against the criterion of an "open and free" internet, as mapped by the Web Foundation, are Saudi Arabia, Vietnam, China, Yemen and Qatar.

"The global connectivity that we now enjoy can deliver enormous gains in freedom of speech and belief. However, it would be naive of me to suggest that it is not also leading to a far more complex and interlinked world of extremist behaviour. I emphasise that I believe that the vast majority of activity online is benign, but we have only to look at the very effective way that ISIS in Iraq has used technology to push out its twisted messages, as well as raise money, to see the other side of the freedoms of the web."

But it was still better to err on the side of freedom of speech, she said.

Dr Bex Lewis, research fellow with Codec, which explores the interfaces between the Bible, the digital world and contemporary culture at Durham University and author of Raising Children in a Digital Age, criticised Lord Sacks for a "technological determinist" position – that the technology is responsible for forcing a person to act in a particular way, rather than giving new opportunities which a person make choices around.

She said: "Social media can be considered like a brick – you can build houses with it, or you can throw it through people's windows. People are doing both with it, as people have always done with every communications medium. Yes, social media allows messages to move faster globally, and those who speak loudest will often be listened to. Social media, however, gives the opportunity to speak back, particularly if people gather together."

Theologian and religious commentator Vicky Beeching, who is carrying out doctoral research in the ethics of the Internet and social media, said:

"It's crucial we remember social media is a tool, and like any tool it can be used for good or for harm. The tool itself must not be blamed; that points the finger in the wrong direction. We must take responsibility for what we do with that tool."

Rather than damning social media and scaremongering about how much harm it can do, Beeching added, we need to recognise its vast potential for good. 

"If religious leaders blame the Internet and encourage their followers to minimise their engagement with it, then people of faith simply become more removed from culture and society and seem increasingly irrelevant and disengaged from the rest of the world," she said. "The Christian faith is about being where people are, showing love, and doing good in those communities - theologically we'd refer to it as 'incarnational living' - and the digital space is such a key community, especially for young people, that religious leaders ignore it or damn it at their peril. I'm always disappointed to hear any faith leader criticising the 'evils' of the Internet, as we need to move further into it as people of faith, not further away from it."