What underlying principle does substantive due process protect?

Substantive due process is a constitutional doctrine that protects certain fundamental rights from government interference. It goes beyond just ensuring fair procedures (which is procedural due process) and focuses on the essence of rights that are considered so fundamental that they cannot be infringed upon without a compelling justification. The principle is rooted in the idea that certain personal liberties are inherent to individual autonomy and dignity.

In this context, the protection of fundamental rights includes various liberties such as the right to marry, the right to raise children, the right to privacy, and other essential freedoms that have been recognized by the courts as fundamental to a person's dignity and autonomy. Therefore, stating that substantive due process protects the fundamental rights of individuals captures the essence of this legal principle.

The other choices represent different legal protections but do not align with the specific focus of substantive due process. For example, the right to free speech is indeed a protected right but falls under the First Amendment instead. Protection from unreasonable searches pertains to the Fourth Amendment, while fair representation in legal matters touches on procedural due process rather than substantive due process. Thus, the correct answer reflects the specific nature of substantive due process in safeguarding fundamental individual rights.