Forums like this usually attract only the young and generally less perceptive individuals.
And fencing the border is usually a solution in their minds to everything. Pakistan's border with Afghanistan is not a very simple issue. This border has ONLY existed on paper and maps, never in reality. Anyone who thinks otherwise is mistaken. Pashtuns live on both sides of this border, and there are literally families on both sides. Inter-marriage is very common. For example: In South Waziristan alone, half the Ahmadzai-Wazir tribe lives on Pakistani side, while the other half lives in what afghans call Paktika province! I personally have friends who are AFGHAN who are Ahmadzai and at the same time Pakistanis who are Ahmadzai!!
So the solution is NOT fencing the border. Thats the shortsighted thing to do. A knee jerk reaction.
Now dont get me wrong, the reason why Karzai(I like to call him Khar-zai) is against the fencing is becuase just like all other Afghans(Be it Pashtun or Farsiwans) they have wet dreams about Pakistani territory being 'greater Afghanistan' or the Afghanistan of Abdali.
But that fear should not force Pakistanis into fencing the border and dividing Pashtuns.
Im not sure why, but Pakistanis have never laid claim to all of Pashtun areas. Im NOT advocating what ISI-Military did in the 90s to squander all the goodwill that Afghans had for Pakistan. Thats NOT the way to go. But Pakistan should make it an open policy that Afghanistan is welcome to join Pakistan as a federating unit as and when they choose. We will never force them, we will never do anything against them. But when Pakistan is developing and sorts out all of its own internal problems with regards to autonomy of all provinces, then they would be more inclined to join us.
The solution to all problems with Afghanistan is in treating them like our true younger brothers. Not interfering in their internal matters and only trying to help them. The Afghans who are already in Pakistan should have been granted Pakistani nationality long long time ago. Thats what all of us Pakistanis expect when we come to US, then why are we hypocritical of that back home?
A big number of our ancestors themselves came from Afghanistan, so why the division now? What we need is not a division but rather an educated and well planned policy of keeping open arms.
Dealing with Taliban is a completely different matter. But to do that, you dont have to fence the border. The solution lies in letting development, education and infrastructure completely develop in those areas. People will automatically leave the Taliban and extremists and work to improve their lives.