I was taught to avoid sentence fragments. And that is what I taught my students. But being as flexible and reasonable as you all know me to be, I would allow the occasional exception. Suppose you have just crafted a paragraph summarizing Kant's views on space and time. I would allow you a 'Thus Kant' as coda. There is no call to be as hidebound as a schoolmarm.
But recently we have been witnessing the fragmentation of the sentence fragment. Example:
Mr. Trump, meantime, is breaking all the china in Washington as he works to reinvent the wheel. Every. Single. Day.
'Every single day' is a sentence fragment. 'Every. Single. Day.' is a sentence fragment fully fragmented.
I am assuming, hopefully, that no one will take the further step of breaking words into their constituent syllables.
Full-on fragmentation cannot be fairly laid at the doorstep of Hemingway any more than conceptual relativism can be fairly laid at the doorstep of Kant. But these gentlemen unwittingly played a role. Or it might be better to say that they set the stage.
I may from now on use Jeff Dunham's 'Walter' puppet to signal language rants. Don't get too excited over my rants. After all, a rant, by definition, involves a certain exaggeration of umbrage.