Not true.
The Durand line doesn't exist, the people immediately on either side don't see it as a barrier and as such, they do not refrain from fighting each others war.
Currently, Afghanistan and Karzai are partly correct.
Areas like North Waziristan are breeding ground for taliban. But which kind of taliban? TTP.
Yes before 2004, the taliban did come to our lands and regroup.
But today, Only one part of FATA is a safe haven and a stronghold.
Whereas half of Afghanistan is out of reach of the government and ANA/ISAF.
Those are the real training grounds. Militants recruit there, they make money from opium there and use that money to buy arms.
In fact, BLA and TTP often regroup in Afghanistan and come to fight another day.
BLA in particular has training camps in Afghanistan.
The NATO troops left the border region back in 2008. Abandonend all outposts and forward bases.
They even left ammunition in forward supply dumps. Since then we've seen militant groups numbering by the hundreds moving along the border. It happens both ways. So it is completely unfair to just blame Pakistan so conveniently.
Now, then the Afghans say... why don't you stop border movement, stop allowing these people on your soil?
I'd say to that, that if we were to do such a thing (which we will never), we would involve ourselves in separating two of the same ethnic group on either side of the border. The refugees that stream into Pakistan, what about them? What would have happened to them if we didn't allow them here.
So three points I'd like to point out here.
- Safe havens exist on either side, in fact more so on their side then ours.
- The ones that are on our side aren't entirely our fault they exist, nor does it mean we have evil intentions.
- Combine the above with the Afghan leaderships anti-Pakistan rhetoric, you will realise that Pakistan is being used as a scapegoat, as an excuse.