The rest of the European Union will refuse to grant Ireland any changes to the Nice Treaty if voters refuse to ratify it in the June 7th referendum, the Taoiseach, Mr Ahern, has said.
Launching Fianna Fail's Yes campaign in the City Hall, Dublin, Mr Ahern said the arguments against ratifying the treaty were "the weakest and flimsiest" ever to have been put forward.
"It would, in my opinion, be disastrous for Ireland to try to opt out of the future development of the EU. All we would do is succeed in marginalising our influence. Countries that hold back have less influence in the EU and find it difficult to be at the heart of European decision-making.
"Other EU countries will not renegotiate anything if we vote No. All we would be doing is creating a temporary crisis, which could only end in deep embarrassment and national humiliation.
"The rest of the Union would either find a means or legal advice for leaving us behind and going ahead without us, or alternatively we would have, like Denmark, to hold a second vote to reverse our earlier decision.
Using some of the strongest language ever against the No campaigners, Mr Ahern said that many were long-term ideological opponents of our EU membership. He added: "It would not matter what terms we obtained. They would still urge us to say No."
They were "ideological bedfellows of the Tory Euro sceptics" and they were "obsessed with old-fashioned concepts of sovereignty", the Taoiseach said, flanked by the Minister for Foreign Affairs, Mr Cowen, and the Minister for Justice Mr O'Donoghue.
"Human rights matter to us, and we should play our part in regional peacekeeping, with whatever other organisations that are present. A No to Nice means less influence and less involvement in our share of humanitarian responsibility."
He was scathing about Christian Solidarity's opposition: "I see nothing Christian and certainly no solidarity in such a stance, only an appeal to a short-sighted selfish materialism."
The Green Party's opposition conflicted with the stance taken by Greens elsewhere in the EU. Finnish Greens supported peacekeeping and crisis management for the EU using national armies.
Sinn Fein's "attachment to neutrality must be of a very recent vintage", he said. "I am naturally impressed when I read about Sinn Fein's opposition to militarism and championship of neutrality.
"But they could still make a big contribution to arms reduction in Ireland on the way to a less militarised Europe. Putting arms beyond use would set a very good example to foreign terrorist groups like ETA," said the Taoiseach."
Last night, Sinn Fein said the Taoiseach was saying that the voters' wishes did not count: "This outrageous statement in itself is a good reason to vote No," said the party's TD, Mr Caoimhghin O Caolain.
The peace and justice group AfrI rejected what it described as the Taoiseach's "slur" against those campaigning for a No vote. It said Mr Ahern implied that by rejecting the treaty Irish people would in some way be rejecting human rights.
"What people who vote for the Treaty of Nice will be rejecting is the militarisation of the EU and the creation of a European army," it said.
