Is Democracy In Pakistan Unconstitutional?

Some say it is…Why? Because the Preamble to the Constitution of Pakistan clearly states

Whereas sovereignty over the entire Universe belongs to Almighty Allah alone,
and the authority to be exercised by the people of Pakistan within the limits prescribed by Him is a sacred trust;
And whereas it is the will of the people of Pakistan to establish an order: -
Wherein the State shall exercise its powers and authority through the chosen representatives of the people;
Wherein the principles of democracy, freedom,equality, tolerance and social justice, as enunciated by Islam, shall be fully observed

Many religious fundamentalists believe that the constitution is violated whenever a military or democratic government takes over because both martial law and democracy are alien to Islam…According to them, democracy does not conform to Islamic principles because Islam is a perfect religion containing laws, express or derivable by ijma (consensus) or ijtihad (exertion), governing the whole field of human existence…Therefore, elections and elected legislatures are unnecessary and unconstitutional…

This got me thinking…What if Zardari signed the peace agreement with the Taliban in Swat only to save his seat and not to bring peace to the area? I wonder if the Pakistanis are as PIL-filing happy as the Indians…Can someone go to court to challenge the validity of a democratic government? If so, has someone done it?

Given the above reading of the preamble, does it mean what the Taliban are doing in Swat (compulsory purdah, no education for women, no entertainment etc.) is constitutional?