The purpose of the constitution was to protect our rights by limiting the powers of the federal government to a very specific set of duties, in the main because the founders believed that the greatest threat to liberty was an unrestrained federal apparatus. A narrow interpretation of the constitution protects us from that threat. The Bill of Rights, passed later, and subsequent amendments, by definition protect specific rights from the federal government only, and as such must be interpreted strictly.
I believe your interpretation of the purpose of the constitution, focusing too narrowly on the Bill of Rights, is incorrect. Specifically, the constitution was intended to spell out the precise and narrow limits of federal power, which is what truly protects individual rights.