First we should keep in mind that establishment is not anti-pakistan. The situation sometimes evolve to a point where the interferance of establishment becomes necessary for the security of the country.
This situation sometime created by inexperienced politicians as mentioned by Saleeqa above and sometimes by corruption of the political figures who want to loot the public exchaqure for purchasing palaces abroad.
Another situation arose in 1977 when the Buttho, otherwise a wise person,
tried to win election by force and, thus, invited the establisment to take control of the country.
In these types of situations the establisment, which is consisted of powerfull Militry & Civil bureaucracy is compelled to play its role for the safety of the country as they are also stalkholders in the power game.
The need of the role of establisment will automatically abolish on the day when a sincere Political Leadership will emerge in Pakistan.