"Government allows it" - must add here the fact that governments are composed of individuals who can be bought, compromised and coerced. Even Pakistan has had these issues since decades and continues to experience it. Heck, even Pakistan has its Tarek Fatehs and what not! There's always a divide present in a society that can be used to create further turmoil. But the fact remains, most of the population has no issues with each other and it would be extremely unwise for our state to sow any hatred between the two nations also. Afghanistan is highly susceptible to foreign meddling and that's a fact Pakistan has to live with for the foreseeable future. It needs management, not a full blown war. Although, aggression is always an option if everything else fails.