The guest post by Andrew Arato on Juan Cole's blog explains the issue very well (my emphasis).
Informed Comment: Arato: The Turkish Constitutional Crisis and the Road Beyond
The makers of the Constitution of 1982 established a dual, semi authoritarian or semi democratic state, with important reserves of power outside the constitution. Starting with the elections of 1983, and then constitutional changes already in 1987 Turgut Özal managed to expand the democratic dimension, leading to a great reform process from 1995 to 2004, that in several rounds that involved the consensual participation of all parliamentary political parties, managed to significantly but by no means completely constitutionalize political powers in the system. Today people stress several military and indeed judicial interventions in this period, that we can see only managed to slow down the rate of change, exclude parties that would reappear in new forms and under new names, but nevertheless confirming the existence of important political centers that could continue to act outside all democratic accountability and constitutional restraints. From 2000-2001 especially, the Turkish parties and governments were under increasing European pressure to eliminate these authoritarian residues, and it was then that the idea of a gradual amendment of 1982 Constitution was replaced by that of a new "civil" or "civilian" Consitutiton. But though the point was not entirely clear either to the European critics or the Turkish participants, unless Turkey had a revolution against the Constitution of 1982, even an entirely new civilian constitution would have to be introduced as a large scale amendment of the still valid basic law.
The Constitution of 1982 has unchangeable provisions that the parliament cannot alter even with 100% of the vote having to do with the republican, secular and unitary character of the state. (Articles 1, 2,3 made unchangeable by Art. 4).
Furthermore even if the Constitutional Court cannot gain much legitimacy in defending the unchangeable provisions of an originally authoritarian Constitution, the legality of its jurisdiction provides it with a vantage point to bring attention to the equally weak legitimacy of a power seeking to alter this constitution on the bases of mere majority will. Both legitimacies are questionable, but the legal position of the Court will remain stronger unless the amendment rule itself were amended by parliament, an act that the Court could again find unconstitutional...because implicitly challenging the unchangeable articles.
Let me point out here, that in most areas imaginable, the AKP has been more democratic, more secular (under pressure) and more europeanist than the Kemalist parties - by far. To even debate this as if it should be an issue in a democratic society, is pointless. Erdogan's party is vastly less religious fundamentalist than extremist christian parties in the Netherlands, say.
It's an irony of history perhaps, but the road to Turkey's democratization passes through the islamic party... The road of excess leads to the palace of wisdom - William Blake
