Tankie is a pejorative label generally applied to authoritarian communists, especially those who support acts of repression by such regimes or their allies. More specifically, the term has been applied to those who express support for one-party Marxist–Leninist socialist republics, whether contemporary or historical.
Denying historical events and refusing to come to terms with their causes and repercussions is not a left or right problem.
You can be as communist as you want but pretending that events with photographic evidence didn't actually happen put you in the same category as moon landing deniers in my book.
And yet so many people believe in religion without a single scientific proof. But yes, I got your point.
For the record there are a lot of shameful events in your history too, but I am sure your own government has done its utmost to hide those facts.
Just that in the US there is a massive anti China and anti Russia propaganda. Do not get me wrong, I don't disagree with a lot of their policies, but the US isn't also spotless and a role model in a lot of ways.
The US has so much red on its ledger it will never be balanced. And there are plenty of apologists for atrocities in our history. They're just as bad as the Chinese or Russian (or pick whatever country you want because they're all guilty to some extent) when they do it.