Where does it say that Pakistan in particular welcomed the move or are you just seeing things. The article says saarc welcomed the proposal and thats about it.
My friend, Pakistan - India rail links are already active. Recently India - Bangladesh trains were inaugurated. Now all this plan does is take it to the next level by connecting these two rail links.
It was a SAARC resolution, and it cannot become a resolution unless ALL members signup on it. Besides this has been on the table for quite a while.
But the important question is why are you against any people-to-people contacts? Why create a wall like the sovites did in Germany? Increased contact will increase understanding among people and remove unfounded suspicion of each other.
Although in the current state of affairs, it would take a while before this train becomes a reality,