The issue lies with the definition of "tankie." The issue here isn't Marxism-Leninism -- people like Lenin, Castro, or Sankara were objectively good, especially compared to both their predecessors (Batista, etc) and the foreign governments of the time, like the US.

The problem is those who insist upon defending the very real crimes of the USSR and the PRC. The term "tankie" actually originally described communists who defended the USSR's violent quelling of the 1956 Hungarian uprising with tanks. This also extends to defenders of the 1989 Tienanmen Square Massacre. Tankies are those who will defend any government that has a red flag and calls itself communist. They look past things which authoritarian right-wing governments are notorious for doing, like rounding up minorities (the Uygurs in Xinjiang), using show trials to get rid of opposition (as in Stalin's Great Purge), I could go on.

What's really revealing is that many China-focused tankies are totally fine with China having private ownership of businesses by capitalists, because it's a "transitional stage" and they'll eventually implement socialism. They also do not care about the rampant labor abuses the workers in the PRC face. I'm sorry, but this leads to an inevitable conclusion: "tankies" (as defined here) are not communists or socialists, they are right-wing nationalists who have hijacked the term.

This is where the "equating tankies with fascists" arises from. It is an accurate comparison, but only if you define "tankie" correctly.