Tankies are simply “people against colonialism” is a new take for me. Pfft.
Well, "tankies" are simply "people who are correct too early", but that does, indeed, include being against colonialism.
But anyway, your question is an obviously false dichotomy.
No dichotomy is presented, other than the implicit "being for/against colonialism" (and, let's be honest, you are firmly for it).
For example, Libertarians and I are both ostensibly against war
Yeeah, no. Let's be honest, you support invaders of Iraq and Afghanistan.
Similarly, by your definition, tankies and I may both be “against colonialism” (and I’m just granting you that for the sake of argument, as I very much think that that is a bullshit take)
Considering that "tankies" were a major force behind decolonisation in the 20th century, your protestations are rather silly.
but we do not agree on the means, the justification of violence, and the authoritarianism needed to oppose it. We are also not friends.
Okay, how do you propose the Global South fights against your empire without violence and "authoritarianism" (i.e. having functioning governments and militaries)?