Quoted text is from Kenneth Keith's introduction to the Constitution of New Zealand (from the Cabinet Manual ).
1. The Constitution Act
The Constitution Act provides for Parliament to have full power to make laws
This is circular reasoning, since the laws of the Cabinet Manual are derived from the Acts that it describes and the Constitution Act is of course one of these.
A description of the nature of democracy is absent from the introduction, and there's nothing there that suggests that democracy is anything more than popular support.
[The convention of respecting the advice of elected representatives] of course incorporates its own limit – one that conforms with democratic principle. If the government loses the support of the House, or if the Prime Minister loses his or her support as the leader of that government, then the ministry or the Prime Minister is likely to change: another party or combination of parties may now have the support of the House, or a new leader may be identified as Prime Minister.
3. Practices and Conventions
The New Zealand constitution is to be found in formal legal documents, in decisions of the courts, and in practices (some of which are described as conventions).
Keith's introduction doesn't say what these practices are other than mentioning those which are described as conventions:
... other major sources of the constitution include:
The conventions of the constitution, which in practice regulate, control and in some cases transform the use of the legal powers arising from the prerogative [of the Queen] or conferred by statute. The most important conventions arise from the democratic character of our constitution.
As previously mentioned, Keith doesn't directly address the issue of what this democratic character actually is.
Constitutional conventions are of critical importance to the working of the constitution, even though they are not enforceable by the courts. In 1982, the Supreme Court of Canada summarised the constitutional position in that country in an equation: constitutional conventions plus constitutional law equal the total constitution of the country.
That basic equation and the democratic character of the main conventions appear clearly in relation to the powers of the Queen and Governor-General under the law. Thus they may appoint Ministers and other holders of important offices...
The democratic character of the main conventions does not "appear clearly" in Keith's introduction, although it could be inferred from it to mean nothing more than popular support.
A balance has to be struck between majority power and minority right, between the sovereignty of the people exercised through Parliament and the rule of the law, and between the right of elected governments to have their policies enacted into law and the protection of fundamental social and constitutional values. The answer cannot always lie with simple majority decision making. Indeed, those with the authority to make majority decisions often themselves recognise that their authority is limited by understandings of what is basic in our society, by convention, by the Treaty of Waitangi, by international obligations and by ideas of fairness and justice.
These assertions are wrong. The injury of the rights of the minority is not mitigated by the power of the majority, and true sovereignty is not in conflict with the rule of law. The right of elected governments to have their policies enacted into law is conditional upon the protection of fundamental social and constitutional values, these elements do not exist in a state of balance. Authority, as a right coupled with the power to act isn't restricted by tradition or by ideas, and the idea that exercising authority could be unjust is an absurdity.