It came as he told the Scottish Parliament’s net zero, energy and transport committee that 39 of the 800 sacked P&O crew live in Scotland.
Scottish Labour MSP Monica Lennon also described the sackings as an “extreme act of corporate terrorism” and called on the chief to resign.
However, Mr Hebblethwaite said: “I have no plans to resign.
"I need to see this through.
"I need to get this business back up on its feet, I need to make it competitive, viable and give us an opportunity to grow in the future”.
But Ms Lennon told him: “You are a failure of a chief executive and most likely right now, in a crowded field, the most hated man in Britain.”
He justified the staff being sacked by saying: “No union could possibly accept our proposal” to make such dramatic changes.
He said these were about a “fundamentally different operating model” rather than changes to rates of pay, but suggested the new crews would only be paid when they worked.
He said: “We are compensating people in full for that failure to consult.”
Mr Hebblethwaite added that crew on the Cairnryan-Larne route will continue to be paid the national minimum wage because it is a domestic UK route.
He stressed: “This is not about Larne-Cairnryan, this is about us having a crew model across the entire organisation that is consistent and competitive.”
He also denied there had been any pressure from the company’s shareholder – Dubai-based DP World – to make the cuts.
The chief said “none of the options” for changes to shore-based staff at Cairnryan considered last year would be taken forward.
Scottish Conservative MSP Liam Kerr asked Mr Hebblethwaite whether he was a “fit and proper person” to discharge his legal duties when he had willfully broken the law – “one of the strongest laws that Parliament had sought to put in place”.
He said: “I did consider that and I believe I have discharged those duties.
"My duties as a director were to make this business viable and I was faced with the option of a programme of change or the closure of the business.
"I took the only route available to me to preserve thousands and thousands of jobs.”
SNP MSP Fiona Hyslop, the committee’s deputy convener, told him: “In my 20 plus years as a member of the Scottish Parliament, I’m not sure I have come across an issue with an employer that has united right across the chamber such hostility.
"The people we represent, even those not in the south of Scotland or in Cairnryan, are absolutely disgusted and dismayed that a company of your reputation has treated people with such disrespect and lack of dignity at work.”
Mr Hebblethwaite said the European Causeway, one of P&O’s ferries on the Cairnryan route, had been found to have 20 defects – 12 technical, four administrative and four crew-related – and was “not ready to return to service yet”.
P&O sailings on the route have remained suspended since the sackings were announced two weeks ago.
Stena Line has continued its services between Loch Ryan Port near Cairnryan and Belfast.