Tankie was coined by trotskyists to insult a slightly different kind of Leninist. Then anarchists picked it up and started calling trotskyists tankies. Now liberals call anarchists tankies. It’s the circle of life, in a few years if you say tankie people will assume you’re talking about Kamala Harris.
From a liberal perspective what’s the difference between MLs having “critical support” for the Soviets or China and anarchists celebrating historical anarchists like Makhno and the CNT-FAI who burned churches and killed kulaks too? If anarchists are online supporting US foreign policy then liberals can assume you’re just a liberal and any claimed anarchism is just larping, but if anybody throws a brick through a Starbucks window that’s tankie authoritarianism stealing rights and freedoms from the Starbucks shareholders.