Many years ago I looked up to Martin McGuinness. Most within the ranks of the Provisional IRA did likewise. When we were moving into our teens, he was the republican Adonis strutting the streets of Derry with martial airs, putting it up the military might of the British with whatever armed prowess he could muster. When he travelled to London in 1972 along with five other IRA commanders for talks with the British government's William Whitelaw, it seemed proof positive that the armed struggle which had whisked the IRA delegation across the Irish Sea would soon keep the British on their own side of it.

Later, when I went to prison to serve a life sentence for a killing carried out on behalf of the IRA and ended up on the blanket protest which led to the hunger strike deaths of 10 republican volunteers including Bobby Sands, we held Martin McGuinness in no less esteem. We regarded him as our chief of staff directing a campaign that was at the time knocking over British soldiers and police officers like pins in a bowling alley.

Watching him earlier this week stand with a British chief constable and British First Minister for a British-run North of Ireland, himself now a British micro minister, I ruminated on the crossover he had made. Standing alongside these implacable opponents of everything he had at one time fought for, he was now denouncing as "traitors" those who had believed him when for years he had proclaimed the IRA the cutting edge of republican resistance. Like a chastened moral dwarf in the land of the giants, there he was screaming "midget" at everybody else.

My respect for him had already shrunk in the intervening years commensurate to his diminishing republican status. I cannot claim surprise, having predicted it both publicly and privately for the past 15 years. The leadership's ambivalent attitude to the non-republican document, the Downing Street Declaration of December 1993, was the writing on the wall. And it spelled "capitulation".

Since then, beginning with an article in Fortnight, the North's main political journal, I sought to question the direction in which the struggle was moving. For the first year things were OK. Wearing an academic hat for cover I could write and comment pretty much as I wanted. By November 1994, the squeeze was on. At an academic conference I had predicted the type of outcome we have today. Summoned to the Sinn Fein headquarters in Belfast by a friend and colleague, I was asked how it was possible for me to have arrived at such a damning indictment of the leadership's strategy. Despite the obvious logic of the trajectory about to be embarked upon, I was rapidly becoming a "thought criminal".

Not to be deterred from thinking, the following year I received the most sustained applause of the day at a packed conference in Dublin when I alerted the audience of about 1,000 party members that there was only one terminus on the road we had taken – defeat. Although Martin McGuinness was at that conference, it was when Gerry Adams also clapped for me that I knew the Judas kiss had been planted on my cheek.

For the next three years I found myself visited by leadership figures and "invited" to be silent. They were wasting their time as much as I was wasting my own in trying to convince my fellow activists of what was afoot.

On the evening of the Good Friday Agreement, Jeremy Paxman asked me in a Belfast television studio what was my problem with the agreement. My response was as terse as it was accurate: it constituted a British declaration of intent to stay in Ireland when the IRA's objective had been to secure a declaration of intent to withdraw. The party leadership was infuriated. That fury percolated down and soon enough nearly everybody else in the party waxed furious. I parted ways with the organisation I had been a member of for 25 years.

The Real IRA had formed some months before the agreement. I never felt the slightest inclination to join up. It appeared inappropriately named. The Make Believe IRA seemed a more accurate way to characterise it. Not because its volunteers lacked commitment or experience, but if the Provisional IRA campaign had failed so completely, there seemed nothing to suggest to me that any other IRA would reverse that situation.

Despite the killings of two British soldiers and one police officer in the past week by the combined gun power of the Real and Continuity IRAs, there is no reason for me to change my mind. Political in motivation and republican in ideology, the IRAs that picked up the baton dropped by the IRA which Martin McGuinness once led have no serious degree of republican political support. They constitute a much less robust militarily efficient organisation than the Provisional IRA.

Their sense of having been sold out by people like Martin McGuinness goes some way towards explaining why they behave as they do. But they are also sustained by the republican tradition of physical force. And within that tradition there is an unshakable belief that so long as there is a British presence in any part of Ireland, republicans will always be justified in bearing arms to strike at Britain and its forces.

Those of us who have "been there and done that" and who can bear testimony to the utter futility of militarism look on events with a mixture of angst and guilt. Angst because of the lives being destroyed; guilt because the logic we preached in the Provisional IRA is their logic. Treading in our footsteps they will secure the same defeat, but for Martin McGuinness to denounce them as traitors for following the example he set for decades is to commit an act of treachery against truth.

Anthony McIntyre is a former IRA prisoner and the author of Good Friday, The Death of Irish Republicanism (http://thepensivequill.am)