Conservative historians of fascism did this to such a great extent that they insisted it was impossible to discuss fascism in a post-war context nonpejoratively

Gregor, who was a closet fascist, and Allardyce, who as far as I can tell was a run-of-the-mill conservative, were the biggest culprits of this, but there have been several "scholars" who insist that calling anything but Mussolini's party and regime fascist is inherently pejorative