Probably "what seems reasonable", although this itself is highly subjective, as demonstrated by the great gulf between what factions in the US consider "reasonable".
There are issues with journalism to be sure. For instance, any coverage of the national debt that only mentions the size of the debt is an abuse of statistics, because the number is meaningless without the context of currency values, interest rates, percentage of GDP, etc.
Nevertheless, the purpose of Journalism, similar to science, is to report on events/phenomenon is the most objective manner possible. (True objectivity is impossible within any given system, including what we call "reality", but that does not negate the legitimacy of the goal.
Thus reasonable analysis of data and application of confidence levels in interpretations is critical.)*
Based on Mr. Mooch's own admission, it is quite reasonable to assume he used vulgarities in reference to this or that person. By contrast, one might be more skeptical of similar hearsay in regards to President Obama, because he doesn't have a track history of public profanity, but might be more open to the hearsay that someone "saw the former President sneaking a cigarette on the patio at the Country Club," because he documented as having this habit early in his presidency.
Part of the problem is that critical faculties differ with each individual, and the embracing of one's biases, which can be a tool, seems rarely tempered by questioning of one's assumptions.
The issue partly relates to the hegemony of subjectivity, which is sometimes abused to cast doubt on scientific positions. (The idea that "evolution is just a theory" demonstrates unequivocally that speaker possesses not even the most basic grasp of what science is per their misunderstanding of "theory", equated in this case with what is known as an "hypothesis".)
So, despite the addage that "Opinions are like #ssholes--everyone's got 'em", not all opinions are equally valid, because some "opinions" are supported by evidence.