Here is an excerpt about judicial activism from an earlier posting entitled Rediscovering Civility and Purpose in America’s Public Discourse:
Many of these aggressive attempts by liberal fundamentalists to redirect societal practices have been done through a hyperactive judiciary. It has been going on for enough decades now and, with our weak knowledge of history, many Americans do not appreciate how judicial activism is a relatively recent phenomenon, it violates the governmental principles upon which our nation was founded, and it has an insidious effect on the relationship between the government and the governed.
Chief Justice Warren Burger elaborated on this in the 1982 case of Plyler v. Doe:

The Constitution does not constitute us as “Platonic Guardians” nor does it vest in this Court the authority to strike down laws because they do not meet our standards of desirable social policy, ‘wisdom,’ or ‘common sense.’…We trespass on the assigned function of the political branches under our structure of limited and separated powers when we assume a policy-making role.

Subsequently, Justice Antonin Scalia reinforced this point in his dissent in the 2003 case of Lawrence v. Texas:

The Court has taken sides in the culture war, departing from its role of assuring, as neutral observer, that the democratic rules of engagement are observed.

In the case of West Virginia State Board of Education v. Barnette nearly 70 years ago, Justice Felix Frankfurter also emphasized how judicial activism is contrary to American principles of government:

As a member of this Court, I am not justified in writing my private notions of policy into the Constitution, no matter how deeply I may cherish them or how mischievous I may deem their disregard. The duty of a judge who must decide which of two claims before the Court should prevail, that of a State to enact and enforce laws within its general competence or that of an individual to refuse obedience because of the demands of his conscience, is not that of the ordinary person. It can never be emphasized too much that one’s own opinion about the wisdom or evil of a law should be excluded altogether when one is doing one’s duty on the bench. The only opinion of our own even looking in that direction that is material is our opinion whether legislators could in reason have enacted such a law…
When Mr. Justice Holmes, speaking for this Court, wrote that “it must be remembered that legislatures are ultimate guardians of the liberties and welfare of the people in quite as great a degree as the courts…” he went to the very essence of our constitutional system and the democratic conception of our society. He did not mean that for only some phase of civil government this Court was not to supplant legislatures and sit in judgment upon the right or wrong of a challenged measure. He was stating the comprehensive judicial duty and role of this Court in our constitutional scheme whenever legislation is sought to be nullified on any ground, namely, that responsibility for legislation lies with legislatures, answerable as they are directly to the people, and this Court’s only and very narrow function is to determine whether within the broad grant of authority vested in legislatures they have exercised a judgment for which reasonable justification can be offered…
This is no dry, technical matter. It cuts deep into one’s conception of the democratic process…

In his book entitled The Uncivil War: How a New Elite is Destroying our Democracy, David Lebedoff offers an explanation about the intent underlying the push for judicial activism:

Many who loudly insist on the appointment of activist judges describe themselves as political “activists,” as well. But how can one possibly endorse both judicial and political activism, unless, of course, political activism has come to mean something different from what the label implies? One who believes in judicial activism can be a political activist only if he or she no longer views political activity as directed toward the achievement of majority support. If one believes that the point of politics is to see that society does what is “right,” regardless of what the public thinks or wants, only then can these two forms of activism indeed be reconciled.

Lebedoff then discusses the eventual consequences of judicial activism:

As those of one political philosophy or another seek to write their own notions into law, with no restraint from themselves or the public, the immigrant wisdom of Justice Frankfurter may be recognized at last for what it really is: a timeless warning that if consent of the governed is not our goal, it will become our memory.

In their book entitled Democracy by Decree: What Happens When Courts Run Government, Ross Sandler and David Schoenbrod note how judicial activism undermines government accountability to the citizenry:

Democracy by decree undermines accountability of government to the voters. Democratic accountability is, in our constitutional scheme, not an unalloyed good. The framers of the U.S. Constitution recognized that a democratically accountable government may reflect bigotry or be inattentive to the people’s needs or rights that they should have. For that reason, the Constitution includes rights and authorizes Congress to enact statutes necessary to ensure that state and local government honor them. These are rights, not aspirational goals dressed up as rights.
As long as rights are honored, everything else, including how the rights are honored, is a question of policy to be left to elected officials. The Constitution and its state and local counterparts set up the ground rules for how policy should be made. These ground rules are designed with careful attention to the potential faults of people and those they elect. The guiding principles are division of power and accountability.
Division of power is required because of distrust of both the people and those whom the people elect. Power is divided, first of all, between those who are empowered to govern and those who are governed. Those who are governed retain the power to vote the elected out of office. The power of those who govern is further divided many ways – between the federal government and the states, and within each level of government among the legislature, the executive, and the courts. Inherent in the whole scheme is that elected officials should bear the responsibility for the key policy choices and must retain the power to change policy.
Although the system is far from perfect, democracy by decree makes it worse. It does not substitute the dispassionate rule of judges for the rule of politicians. Decisions by controlling groups are politics in a different form. By hiding ordinary politics behind the robes of judges, democracy by decree makes government less accountable and therefore less responsive. Judicial reason does not supplant politics. Instead, the courts become political.

It is only through the “messiness” of a reasoned public discourse that a broad societal consensus can be achieved on major issues. Judicial activism short-circuits that process, to the detriment of our democratic institutions and habits.
This issue has been discussed in previous postings:
Are You an Originalist?
How Original Intent Does Not Equal Conservative Judicial Activism
“We Are Going To Go To War Over This”
“The Supreme Court Has Converted Itself From a Legal Institution to a Political One”
Relinking Constitutional Law & Jurisprudence to the Constitution
Rediscovering Proper Judicial Reasoning