Tankies don’t usually believe that Stalin or Mao “did nothing wrong,” although many do use that phrase for effect (this is the internet, remember). We believe that Stalin and Mao were committed socialists who, despite their mistakes, did much more for humanity than most of the…
There's also a stereotype of leftists needing several paragraphs to explain their ideas when the right wing can get people frothing with mere catchphrases. The balance between nuance and people actually listening is a tough one.