When Did Poetry Become So Nice?

Evan Gottlieb has an answer:

In many ways, it was the Victorians who, reassessing and largely whitewashing the Romantic legacy, transformed poetry from the record of real life sought by Wordsworth to "the best which has been thought and said" touted by poet-critics like Matthew Arnold as a replacement for the waning power of organized religion. In this "improving" spirit, for example, the poetry of Percy Shelley—probably Wordsworth's most rebellious heir—was cleaned up and made fit for drawing room readings, such that he was known for many generations as the poet of ethereal verses like "To a Skylark," rather than as the author of much more strident, political poems like "The Masque of Anarchy" and "Song to the Men of England."

He singles out a favourite troublemaker:

An exciting blend of shamelessness, cynicism, and lust is the calling card of the 17th-century libertine poet John Wilmot, the Second Earl of Rochester, whose exuberant poems detailing his sexual conquests, both male and female, bear titles like "Signior Dildo" and "The Disabled Debauchee." Rochester's verses still contain plenty of power to make modern readers gasp, chuckle, and shake our heads in a combination of disapproval, disbelief, and—let's be honest—envy at his frankness, if not also at his exploits.

Tony Hoagland reminds us of why "talking mean" in poetry matters:

There is truth-telling in meanness, but that is not all of it. Meanness is also an aesthetic asset for its flavor of danger. Nothing wakes us up like menace—Menace refreshes. When a poem becomes aggressive, it rouses an excitement in us, in part because we see that someone has broken their social shackles. We feel intoxicated by that outlaw freedom, and we covet it for ourselves.