Conor Friedersdorf lists some various conceptions of the role of an opinion journalist:

The purpose of opinion journalism is...
1) make money.
2) attract an audience.
3) influence people.
4) ... to generate ideas.
5) advance conversations.
6) help air different sides of a debate.
7) help the political prospects of your ideological coalition.
8) disparage ideological adversaries.
9) raise the political price of trying you or your former colleagues for war crimes.
10) earn a living as a writer.
11) get on television.
12) produce an intellectually honest argument.
13) accrue social prestige.

LOL on #9.

As I see it, #12 -- "to produce an intellectually honest argument" -- is the correct answer. I'd put it slightly differently: to explain the world as I see it. Understanding the world requires digesting facts, but it can't be done entirely through digesting facts -- it requires some degree of normative judgments as well. That is what opinion journalism should do. You can be in this business to influence people, but then you're in a very tricky position when it comes to writing opinions that might have the effect of influencing people to act contrary to the way you want them to act.

Now, I see calling out dishonest or unpersuasive arguments as a major part of producing intellectually honest arguments. (It's the "argument" part of "honest arguments.") When you do that enough, it can start to resemble #8, disparaging ideological adversaries. But I view disparagement as a side effect rather than the primary prupose. It is fun, though.