The HBO drama was recently renewed for a second season, but has received a mixed reaction from critics.
"I think it's aspirational," Waterston - who plays Charlie Skinner - told the Los Angeles Times.
"I would only think people would use that word [preachy] in order to dismiss it because there's a lot of opinion in it. God help us, isn't there a lot of opinion in the talking-heads world of cable television?"
The 71-year-old actor added that it is "lying" in the news business that "drives [series creator] Aaron [Sorkin] nuts".
"That's a completely bipartisan and unpreachy thing, if you ask me," he argued. "It seems to me that that's coming from some place much more visceral than where people preach from."
The Newsroom continues on Sundays at 10/9c on HBO. The series will make its UK debut on Tuesday, July 10 at 10pm on Sky Atlantic.
