The Irish border backstop represents a baseline guarantee over the future relationship between the UK and the EU, the Irish Taoiseach said.
Having a withdrawal agreement without the insurance policy mechanism to keep the frontier open if future talks foundered would not provide certainty but would just leave the matter to be dealt with years later, Leo Varadkar added.
He addressed the West Belfast Feile festival on Tuesday evening.
What the backstop has been able to do is set a floor on that future relationship
The Irish premier said: “All this is about, in my view, is setting a floor on the future relationship.
“Because we know once the UK leaves the EU, we are going to have to negotiate a free trade agreement, we are going to have to negotiate a new economic and security partnership and we are going to want to.
“What the backstop has been able to do is set a floor on that future relationship.
“It gives us the guarantee that, no matter what else may happen as a consequence of Brexit, we won’t have any restrictions north/south or east/west.”
Mr Varadkar has been a staunch supporter of the proposed backstop, which was agreed between the EU and former UK prime minister Theresa May’s government.
Parliament’s opposition to the measure saw Mrs May fail to get her proposal into law earlier this year.
Traders in Northern Ireland want some mechanism to keep the invisible land border open following Brexit and preserve the current frictionless arrangements.
The backstop would mean the UK and Northern Ireland following EU rules relating to matters such as customs and trade.
Unionists believe it could threaten the integrity of the UK if Northern Ireland were to diverge from Great Britain.
Brexiteers feel it would keep the UK chained to the bloc indefinitely and could prevent it from striking trade deals with other parts of the world.
Mr Varadkar said: “I think there has been a bit of revisionism recently almost suggesting that the Withdrawal Agreement, including the backstop, was something invented in Brussels or Dublin, or something that we tried to impose on the House of Commons.”
He referenced the recent change of ministers in London.
The Taoiseach added: “I was there for the past two years and I know that the Withdrawal Agreement and backstop was something that we co-designed and developed and negotiated.
“There were a lot of trade-offs with Prime Minister May and her government.”
He said that closed off many options and the Withdrawal Agreement was very much crafted around those red lines and represented the best outcome they could reach.
Mr Varadkar met firms in Northern Ireland on Tuesday and said the business community wanted certainty about the future, adding that leaving with no deal did not do that.
He said: “Having a withdrawal agreement without the backstop does not give them certainty either because it just leaves those important questions to be sorted out in a two or three-year transition period.”
That convinced him of the need to ensure the backstop remained part of the withdrawal agreement, he said.
Mr Varadkar said he expected Prime Minister Boris Johnson would take up his invitation to visit Dublin in the next couple of weeks.
“I don’t think we are being intransigent, what I think is somewhat disappointing anyway is this view that we seem to be getting from London that we won’t talk to the EU until you drop the backstop.
“That is not a good starting point for further talks but we are willing to talk.”