The implication is that it will bring about the return of the IRA with their guns and bombs.
A little lesson in recent history is needed on this, as it was rewritten almost before it had finished taking place.
In the early to mid 90,s the IRA were in deep trouble. The money from the U.S to fund their campaign was quickly drying up. The leadership (Mad dog McGuiness in particular) knew the UK powers that be had been investigating their crimes, and it wasn't going to be long before they were behind bars for life for many murders.
The community they claimed to represent was sick and tired of the violence and support had dwindled away.
The leadership sent a message, via an intermediary to the UK Govt. saying that they wanted to cease the violent campaign but wanted a dignified way out, rather than a surrender.
Talks began behind the scenes along these lines, but then Major lost the election and B. liar was in charge.
He approached the whole thing with a "Hi guys, would would you like me to do for you" attitude, and Adams and McGuiness saw a great opportunity, which is why they nicknamed him The idiot, behind his back.
Blair gave them so much that he didnt need to (pretty much what Mayhem is doing with the EU at the moment) and the end result was the ludicrous Good Friday agreement. Which allowed all the terrorists out of prison, even those serving life sentences for mass murder. Gave "get out of jail cards to those who weren't in prison but should be. And put the IRA leadership in Govt. in Northern Ireland.
Coincidently, I was in Belfast visiting the family the day it was signed, and remember how suspicious a lot of people were, but agreed to give it a try to end the violence.
When some time had passed and it became clear exactly what they had signed up to people were livid, but it was too late by then.
Point is, the IRA aren't coming back. They surrendered in all but name, and the world has changed so much since then that they would get almost no support from previous supporters, inside or outside Ireland if they wanted to try to make a comeback.
The constant veiled threat of them coming back of we don't do what the EU and Dublin demand about the border is nothing short of sick and makes my blood boil.