Here's a userscript to apply it automatically, and show all the extra whitespaces people put in their comments. (There aren't many.)

  // ==UserScript==
  // @name         HN comments show whitespace
  // @description  Changes HackerNews CSS to show comments with original whitesapaces
  // @match        https://news.ycombinator.com/*
  // @run-at       document-body
  // @grant        none
  // ==/UserScript==
  
  // HN inserts a newline after <pre> so formatted code blocks have a whole newline after them
  // but we can remove that extra space with negative margin
  
  const HN_noformat_CSS_rule = `
  div.commtext.c00 {
    white-space: pre-wrap !important;
  }
  div.commtext.c00 > pre {  
    margin-bottom: -.25em !important;
  }
  `;
  
  let myStyleHolder = document.createElement('style');
  myStyleHolder.textContent = HN_noformat_CSS_rule;
  document.head.appendChild(myStyleHolder);