Judicial activism has become a universal pejorative, a rare point of agreement between red and blue America. Conservatives and liberals alike condemn courts for overturning policy decisions they support. Both sides would reduce the judiciary’s constitutional scrutiny of the actions of other branches of government — a role it exercises not too much but far too little.

To be sure, courts deserve criticism when they exercise legislative or executive powers — ordering taxes to be raised, assuming control over school systems or prisons, or as the Supreme Court did yesterday, giving regulatory agencies broad lawmaking authority. But better to call this behavior what it really is, which is not “activism” but lawlessness. By contrast, judicial activism — defined as courts holding the president, Congress, and state and local governments to their constitutional boundaries — is essential to protecting individual liberty and the rule of law.

Judicial review, the power to invalidate unconstitutional laws, was essential to the scheme of republican government established by our Constitution. The courts, declared James Madison, would provide “an impenetrable bulwark against every assumption of power in the executive and legislative” branches, and “will naturally be led to resist every encroachment of rights expressly stipulated for in the constitution by the declaration of rights.”

Conservatives have long attacked judicial activism; more recently liberals have joined the chorus. Now that the welfare state and other cherished policy objectives are enshrined in law, many liberals heed Justice Stephen Breyer’s call for “judicial modesty.” The liberals’ newfound self‐​restraint permeated the Supreme Court confirmation hearings of John Roberts and Samuel Alito, who were accused of predilections toward conservative judicial activism.

Liberal critics cite statistics showing that the Supreme Court under Chief Justice William Rehnquist was more activist in invalidating federal laws than any of its predecessors. True. But the number of decisions striking down executive and legislative actions pales in comparison to the growth of federal laws and regulations during the same period. It took 169 years from the founding for the federal code of laws to reach 11,472 pages — and only four decades more for that number to quadruple. In 1960, the Code of Federal Regulations numbered 22,000 pages; today that number has grown by more than 700%.

Advocates of judicial deference contend that courts are ill‐​equipped to second‐​guess legislative determinations. If legislators carefully pondered the merits and constitutionality of legislation, that argument might have merit. But our legislators rarely even read the complex bills they pass, which all too often are manipulated by outside interests. Judges, by contrast, carefully sift through competing evidence presented by both sides. And they should. Courts that merely rubber‐​stamp legislation or executive branch decisions out of bland, or blind, “deference” evade their essential constitutional role.

Moreover, judicial deference to “democratic processes” is beside the point, given the proliferation of laws and regulations created by bureaucrats who are not in any meaningful way democratically accountable. And not only at the federal level.

The most explosive growth in local governments in recent decades has occurred in special districts and regional authorities that typically are accountable (if at all) to politicians, not voters. Ironically, courts typically defer to the “expertise” of regulatory bodies, rather than carefully scrutinizing their actions for compliance, not only with constitutional commands, but even to the vast legislative and executive powers that have been delegated to them.

At bottom, liberal and conservative attacks on judicial activism are hopelessly subjective and inconsistent. Take two cases from the 1990s. In one, the U.S. Supreme Court struck down a Colorado law that forbade local governments from enacting antidiscrimination laws that protected homosexuals. In another, the Court struck down a New Jersey law that forbade the Boy Scouts from excluding homosexuals. In both cases, the Court protected freedom of association, finding an exercise of democratic power at the state level unconstitutional. Similar cases, similar principles, identical results.

Most liberals supported the result in the first case, condemning the second as judicial activism; most conservatives did precisely the opposite. What critics on both left and right really object to is the neutral application of constitutional principles when it hampers their own desired policy outcomes.

While judicial activism is the subject of spirited attack, the far greater problem is judicial abdication of its core constitutional duty to protect individual rights. Courts routinely apply a presumption of constitutionality to most governmental enactments that skews the playing field against individuals whose rights are violated. Far worse, courts have read out of the Constitution vitally important protections of individual rights, such as the constraints against government interference with the sanctity of contract and the privileges or immunities of citizenship.

As the framers understood, these are not esoteric issues, but affect in the most tangible way the real rights of real people. In its infamous Kelo decision, the Supreme Court expanded the power of eminent domain beyond its constitutional limitation — public use — to the nebulous realm of public benefit. So “deference” to legislators and other government entities results in a free‐​for‐​all, with private property taken from citizen A and transferred to citizen B — precisely the danger against which the framers tried to protect us.

As with property, so too with traditional common‐​law liberties, such as the right to work in a lawful occupation. The hard lessons of judicial deference and abdication are taught, over and over again in this country.

When Leroy Jones and his partners tried to establish a new taxicab company in Denver, they had everything they needed: experience as drivers, untapped market demand, and capital; everything, that is, except a “certificate of public convenience and necessity” from the Colorado Public Utilities Commission. When they applied, they received the same response as every new taxicab applicant since World War II: application denied.

Mr. Jones challenged the power of this government commission to maintain a monopoly, but he came away empty‐​handed. Unfortunately, the “privileges or immunities” clause of the Constitution’s 14th Amendment — designed precisely to protect freedom of enterprise from government interference — had been eviscerated more than a century ago in the Slaughterhouse Cases of 1873. (In these cases, the Supreme Court, by a 5–4 majority, upheld a state government monopoly of slaughterhouses in New Orleans that put scores of butchers out of business and nullified the constitutional protection of the clause.)

No thanks to the courts, at least in Mr. Jones’s case, the media coverage shamed regulators into giving him a permit to establish a taxicab company.

Properly wielded, a court gavel can be David’s hammer against the Goliath of big government. Among our governmental institutions, courts alone are designed to protect the individual against the tyranny of the majority — and against special interest groups with outsized influence.

The Rehnquist Court began to restrain unconstitutional exercise of government power in areas such as private property rights, equal protection, commerce and federalism that previous courts had allowed to run riot. But toward the end of the Rehnquist era its fervor began to subside. It remains to be seen whether the Roberts Court will proceed to boldly protect liberty, as the Constitution intended.

We all have a stake in seeing that it does, for as government inexorably expands, our freedom depends on the willingness of courts to rein in its excesses. For better or worse, the courts are the last line of defense against government running roughshod over individual liberty. When judges swear fealty to the Constitution, they must be mindful of the danger of exceeding the proper confines of judicial power, but as well the even greater danger of abdicating it.