The Post article is an op-ed, not something written by the editorial board. I’d prefer that newspapers feel free to publish a wide range of views without readers ascribing those views to the paper (I.e., the newsroom or editorial board).
Sure. But it's under their banner. They edit the op ed and can demand unsubstantiated claims be substantiated or removed. Otherwise it really is no better than done racist blog.
A case that can't be made without facts that can't be stood up shouldn't be made in any newspaper that values it's reputation.