Constitutional rights are useful up to a point, but they do not serve to guarantee much more than what could be called the bourgeois conception of freedom. According to the bourgeois conception, a "free" man is essentially an element of a social machine and has only a certain set of prescribed and delimited freedoms; freedoms that are designed to serve the needs of the social machine more than those of the individual.
To ask about the 'source' of rights or morals assumes an erreous conclusion. To ask about the source of morals is to assume that such a source exists. As if it existed outside of human constructed systems. The 'source' is the human ability to learn from experience and to entrench rights in our laws and in our consciousness. Our rights come from our long history of wrongs.
The preservation of peace and the guaranteeing of man's basic freedoms and rights require courage and eternal vigilance: courage to speak and act - and if necessary, to suffer and die - for truth and justice; eternal vigilance, that the least transgression of international morality shall not go undetected and unremedied.
The Declaration of Independence has been called, with some justice, the most revolutionary document in human history, in that it placed the individual person first in the political scheme of things and made the legitimacy of governments and ruling classes contingent on their success at preserving individual rights.