Why is a constitutional republic preferable to a democracy?
A democracy is where a majority dictates to the minority whether or not your rights will be protected.
A constitutional republic is based on the concept of the sovereign individual. We individuals are the source of political power and we loan our power to representatives and we delegate our right to self-defense to the judiciary and the military.
Besides democracy, other forms of government can violate individual rights:
The very foundation of socialism is the violation of rights; particularly property rights. Statism, monarchy, feudalism all rest on an arbitrary power relationship that places the individual at the mercy of a ruler. Democracy is no better because a democratic form of government offers no guarantee that an individual's rights will be protected.
The proper form of government for a free people is constructed to absolutely protect individual rights regardless of the shifting mood of the masses. That protection is not guaranteed by any other form of government than a constitutional republic.