A time not so long ago, public intellectuals in Western democracies loudly denounced war and imperialism, oppression and the violation of universal values (truth, justice, etc) whenever and wherever they occurred.
True, critical/oppositional intellectuals were always few and far between in the modern Western era, but there were always giants in our midst whose voice and status were not only revered by a fair chunk of the citizenry, but, in some cases, produced fear and even awe among the members of the ruling class.    
In this context, well known 20th-century names like John Dewey, Bertrand Russell, George Orwell, Jean-Paul Sartre, and Albert Camus easily pop to mind. They were thinkers of immense intellectual prowess, independent of those in power, who spoke out against social evils and abuses of power. 
Equally important, the stance they took on public issues mattered because it mobilised thousands of ordinary citizens to participate in political advocacy.
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'The right side of history'
Scientists and artists like Albert Einstein and Pablo Picasso, respectively, can easily be included in the above list as they were also public figures who were interested in issues of common concern and did not hesitate to stand on what they believed to be "the right side of history": Einstein consistently supported anti-war movements and highlighted the dangers of nuclear war while Picasso was a committed anti-fascist.
Much closer to our own time, the list of names of world-renowned critical/oppositional intellectuals that stand out has been getting worriedly smaller and smaller, especially since most of them have passed away (Harold Pinter, Howard Zinn, Edward Said, Pierre Bourdieu). 
Indeed, the world's greatest critical/oppositional intellectual who is still alive is undoubtedly MIT Professor Emeritus of Linguistics Noam Chomsky, and he clearly represents a dying breed. When he passes away, there is no one able to fill his shoes.
Notions such as democracy, social justice, equality, and the common good have taken a back seat to a crude individualism which is driven by consumerism, social apathy and self-aggrandisement...

The reality is that, with small exceptions, today's Western world is dominated by functional/conformist intellectuals, ie, thinkers whose mission is not to inform the public about social evils, abuses of power and the threat they pose to freedom, democracy, and dignity, but to enhance their own careers and material wealth by preserving and reproducing the existing order and the dominant power relations. 
Functional/conformist intellectuals focus on narrow, highly specialised and technical areas, and do not dare to challenge the status quo or speak out against social evils out of fear of losing their job, being denied tenure and promotion, or not having access to grants.
Conformist intellectuals
If asked, conformist intellectuals will probably say that it is not their duty and responsibility to speak out against, say, US militarism, imperial policies and the destruction of entire nations (Iraq, Libya, Syria), the abomination known as Guantanamo Bay prison, police and state violence, Israeli oppression of Palestinians, predatory capitalism and Wall Street crimes, authoritarianism and inequality.   
But the true explanation is that they are simply cowards.
Those members of society with the best access to knowledge do have a duty and responsibility to speak out and take action to support peace, freedom, democracy, and the common good. 
As Chomsky wrote in his famous essay: "The Responsibility of Intellectuals", published in The New York Review of Books on February 23, 1967: "Intellectuals are in a position to expose the lies of governments, to analyse actions according to their causes and motives and often hidden intentions. In the Western world, at least, they have the power that comes from political liberty, from access to information and freedom of expression. For a privileged minority, Western democracy provides the leisure, the facilities, and the training to seek the truth lying hidden behind the veil of distortion and misrepresentation, ideology and class interest, through which the events of current history are presented to us."
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The disappearance of critical intellectuals can be attributed to several interrelated developments. 
For starters, universities have abandoned their traditional role of preparing students to be caring, active citizens, and, instead, aim almost exclusively towards preparing them for the global marketplace. Accordingly, most universities produce professionals these days rather than graduates as critically engaged citizens who will play a leading role in their communities and in the struggle for a better world.
Decline of political advocacy
The absorption of writers and artists into the academic world has also enhanced the trend towards the disappearance of the critical/oppositional intellectual.
With neoliberalism as the dominant ideology shaping our world today, notions such as democracy, social justice, equality, and the common good have taken a back seat to a crude individualism which is driven by consumerism, social apathy and self-aggrandisement, thus further reinforcing the decline of political advocacy and the divorce of the intellectual elite from the pursuit of universal values like truth, justice and peace.
To the list of factors contributing to the rapid disappearance of engaged political cultures in Western societies with critical/oppositional intellectuals at the helm, one must add the corporate takeover of mass media whose main mission is the manipulation of public opinion and the shaping of a politically apathetic culture.
The dominance of neoliberal ideology combined with the disappearance of critical/oppositional intellectuals spell a bleak future for Western democracy and its cherished values.   
In fact, silencing those voices that speak out against social evils and the abuses of power seems to have become the norm.   
Indeed, how far we seem to have come from the time when leading critical/oppositional intellectuals not only challenged the status quo, but actually had the capacity to inspire awe to the status quo itself, thus prompting someone like French President Charles de Gaulle to mock at the idea of arresting Jean Paul Sartre for inspiring rebellion by saying: "One does not arrest Voltaire."
C J Polychroniou is a political economist/political scientist who has taught and worked for many years in universities and research centres in Europe and the United States.