Spending billions of pounds on renewing the Trident nuclear weapon system would be immoral, according to the SNP.
The decision on Trident is likely to be made in the next two years
The claim came in an SNP-led Holyrood debate on the renewal of Trident, an issue reserved to Westminster.
It follows a march on the parliament last week by peace campaigners and church leaders.
However, Labour and Conservative MSPs believe Trident would play a valuable part in international talks to rid the world of nuclear weapons.
The SNP's Roseanna Cunningham said that when maintenance costs were taken into account, the real cost of replacing Trident was £76bn rather than the £25bn which has been talked about.
She called for a national debate but resented Labour's suggestion that it should be confined to Westminster.
Ms Cunningham said there was no moral justification for nuclear weapons, especially when Britain was trying to persuade other nations not to acquire them.
"If we are not using them, why do we continue to buy them? And if we continue to buy them and stockpile, why do we believe we can continue to tell others that they should not do the same?" she said.
"When we brandish weapons whose only purpose is mass and indiscriminate slaughter, we give up all right to preach to others about the morality of the choices they might make."
Labour's Jackie Ballie said the SNP had not thought through how it was going to eradicate the world's nuclear weapons and what it would do with the existing Trident submarine base at Faslane, where 7,000 people were employed.
"It is a staggering number of jobs. I've been accused in the past of using that as some kind of excuse for keeping nuclear weapons," she said.
"Far from it, those are the facts. It might be uncomfortable for the SNP but they are very real and must be addressed."
Mike Rumbles from the Liberal Democrats criticised Chancellor Gordon Brown for pre-empting the debate on Trident.
Religious and peace campaigners have protested against Trident
Conservative Phil Gallie said he hoped there would be a vote at Westminster, where the final decision would be made, some time in the next two years.
The Green Party has expressed concern over any impact on workers at Faslane or Coulport.
Chris Ballance, the party's spokesman on nuclear issues, said: "Government must engage with workers and trade unions now to plan for transferring the skills and experience of the workforce into other industries.
"We need to stop throwing tens of billions of pounds into a weapons system aimed at a threat which no longer exists."
Socialist MSP Rosie Kane said: "This parliament needs to speak out. To say it is a reserved matter, a big boy did it and ran away, is no excuse.
"If they had the will, they could speak up."