David Cameron admitted he finds it "painful" to work with former IRA chief Martin McGuinness today as he defended the Bloody Sunday Inquiry.
But the Prime Minister insisted compromises such as the rehabilitation of the Northern Ireland Deputy First Minister were a "price worth paying" for peace.
"The Good Friday Agreement was very painful because it did mean that people who had done appalling things were let out of prison.
"But in the end the government, and I supported them, thought that it was right to make that proposal to try to end the conflict.
"As a result the IRA did agree to end the war, as they put it, to put their weapons beyond use, pursue peaceful means."
Mr Cameron referred to senior Tory figures Ian Gow and Airey Neave, who were both killed in republican attacks.
"I find it personally quite painful when I think of Ian Gow or Airey Neave - Airey was the first MP who ever represented me in Parliament.
"I do find it painful that I now sometimes sit around a table with Martin McGuinness and I think about what that man did.
"But everyone has to come to terms with that because that is the price we are paying for peace, and it is a price that is worth paying, because peace is so much better than the alternative."
The premier insisted that the Bloody Sunday Inquiry had been necessary despite its huge costs - and stressed that prosecutions were still possible in relation to other incidents during the Troubles.
"We have to ask ourselves with Bloody Sunday, when 13 people were killed on that one day, is it right to have an inquiry and get to the bottom of what happened on that very black day in British history.
"I think it is right. That doesn't in any way detract from other people who suffered."