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