In the 1800s, as the mass media began to gather influence mostly via newspapers, the political rulers were wary of 'public opinion' - it seems that they felt that, at times, the country needed to be led in the direction of this thing - public opinion - even against the politician's wishes.
What was it, and why did politicians been led by it? My assumption is that public opinion was, more or less, 'what people are talking about' - more exactly, what the people who might cause trouble were talking about. What people talked about was difficult for the government to control back then - and it took a long time - weeks rather than days - for any politcal influence to be brought to bear. Meanwhile there might be riots, strikes, machine-breaking... and this could spread faster than the ability of the governent to suppress it.
Nowadays I don't hear public opinion mentioned in the way it was in my youth - governments are no longer bothered by it. Indeed, nowadays public opinion (so far as it is mentioned) serves the opposite role than it did in the past. In the past it forced governments to do what they did not want to do; nowadays public opinion is only ever invoked as an excuse for governments to do what they anyway want to do - when some particular person or group is disagreeing.
The reasons for the decline in the status of public opinion is straightforward enough - we live in a world where the media controls politics, and the modern mass media can change what people are talking about in minutes rather than weeks.
And a world in which the public are (willingly) addicted to the mass media - so whatever is in the mass media, is also and instantly in the minds of the public - and not much else is in their minds; because so much of each person's discretionary times and energy is spent in servicing their addiction.
In a world of mass media addiction and domination; the only 'danger' to the mass media view carrying the day comes from disunity among the mass media - internal dissent - which is why so much of the mass media comprises (in effect) journalists talking to journalists.
When the mass media agree on 'the message' then effective public opinion will also agree, instantly - because the public's heads are filled by the mass media, 24/7. The unified-media 'talking points' are what the public talks about, always and instantly: end of story.
And this is what people want: this is what public opinion wants. This is how modern society wants it to be. Just as junkies want more heroin, the public want more mass media - just as junkies want to be high all the time, the public want the mass media all the time.
People slog away at soul-destroying jobs to get the money they need to buy the new technological equipment and access that ensures that they can best stay plugged-into the mass media for every waking moment outside of those soul-destroying jobs.
This is Brave New World, not 1984, because there is so little resistance to the techno-utopia; because the means of our enslavement (and damnation) is not just accepted, not merely loving embraced - but actively-sought and vehemently-defended.
See also: http://addictedtodistraction.blogspot.co.uk/