why most americans believe that the media have a negative impact on the country

no news here. 

it's no surprise that most americans believe that the media have a negative impact on the country.

"... new survey from the Pew Research Center finds that two-thirds of Americans now say the news media has had a 'negative impact on the U.S."--rating the press at the bottom of a list of national institutions which includes churches, colleges and labor unions. ... The national survey found that 63 percent of the respondents gave a thumbs-down on the media and its influence on 'the way things are going' in the nation."

Two-thirds of Americans say news media has a negative impact on the nation: Poll - Washington Times

it's not surprising at all--a third of the country doesn't know Walter Cronkite, whose last news broadcast was in 1981. If only those who were born before 1965 had been polled, then the 2/3 would be more like 100%.

image by Rob Bogaerts

File:Walter Cronkite (1985).jpg - Wikimedia Commons

For those who were born after 1965, Walter Cronkite was anchor for the CBS Evening News from 1962 to 1981. Walter reported the news. Unlike Fox News, which advertises "we report, you decide", and then has a battalion of staff and outside "experts" to tell you what you should decide, 50 years ago CBS news reported the news without the benefit of "talking heads" to "interpret" the news for its viewers.

"Fair, balanced and unafraid" Fox crows. Really? How many people believe that Fox News is fair and balanced? Do those who believe that Fox News is fair and balanced also believe that CNN is fair and balanced? And, do those who believe that CNN is unbiased also believe that Fox News is unbiased? negative.

Obvious bias in the news media isn't restricted to Fox, CNN and cable TV however. Virtually every TV network, newspaper, magazine and radio news program is biased. The internet is so grossly biased that "fake news" has become part of our regular vocabulary. 

unfortunately, the media's sad current state has resulted in most Americans, even some who were born after the Walter Cronkite era, believing that the media has a negative impact on our country. 

sadly, the Walter Cronkite era is gone forever.