An article on Reuters sums up why negotiating with the Taliban is impossible. According the article Muslim extremism has changed: a few years ago it was about specific causes: the Indian "occupation" of Kashmir, the ignored elections in Algeria, etc. But now it is just about creating chaos all over the world in the hope that that will prepare the road for the Islamic Caliphate.
It reminds me of the anarchistic movement at the start of the 20th century in Europe.
I don't agree with the whole of the article. Having foreign fighters has several advantages that the article fails to name. It gives the organisation access to foreign political and financial support. And it gives the local fighters a sense of belonging: they are no longer fighters for a lost cause in a forgotten corner of the earth but people elsewhere care about them. But this does not mean that each such organization actually will take part in that global struggle.