New York Times writer (and former editor) Bill Keller printed a series of letters exchanged between him and muckraking journalist Glenn Greenwald. It’s a little long, but well worth reading.
I don’t think of it as reporters pretending they have no opinions. I think of it as reporters, as an occupational discipline, suspending their opinions and letting the evidence speak for itself. And it matters that this is not just an individual exercise, but an institutional discipline, with editors who are tasked to challenge writers if they have given short shrift to contrary facts or arguments readers might want to know.
The thing is, once you have publicly declared your “subjective assumptions and political values,” it’s human nature to want to defend them, and it becomes tempting to omit or minimize facts, or frame the argument, in ways that support your declared viewpoint.