Someone asked a very similar question the other day. Here's a link to my reply, in case you're interested: https://lemmygrad.ml/comment/559425. And related to this, I also recently wrote something about the need to defend a revolution: https://lemmygrad.ml/comment/565520.
To answer your questions…
I don't self identify as a tankie and I'm not sure that anyone does. It seems to be a broad term used by anti-communists so that they don't have to do the hard work of engaging with what's being said.
If anyone does call me a tankie it's because I'm a Marxist-Leninist (ML). MLs are historical materialists. This involves a way of looking at the world that was first developed by Marx and Engels. Historical materialism (himat/histmat) applies dialectical materialism (dimat/diamat) to human society, treating reality as interrelated processes, not things.
This methodology is opposed to bourgeois ways of thinking and of other 'vulgar' strains of Marxism. As MLs interpret the world according to himat, they say things that can be incomprehensible to those who don't know understand dialectics or materialism.
Chomsky is a good example. He's a renowned prof at a top university but he admits that he doesn't understand himat and has never tried to. How can one possibly deal with one's opponents arguments in good faith without even trying to understand where they're coming from? An honest theoretician would admit that he's simply talking past his opposition, as might e.g. Ronald Dworkin or John Finnis (IIRC). Not Chomsky, who gives the perception that he's understood his opponents before dismissing them. Anyway, I digress.
I don’t think communism is the answer, because I don’t think it’s a path we can walk without first curing the disease, but the guiding concepts resonate with me.
In The German Ideology, Marx and Engels wrote:
We call communism the real movement which abolishes the present state of things.
I won't say that you're a tankie, lol, but you're in agreement with the MLs. Following Marx and Engels, communism is the process of curing the disease.
It is often said that communism is the end goal. In a way, this is true. But we need to look a bit further and apply himat to fully understand the position. According to himat, all relations/processes are internally contradictory (himat still complies with formal logic).
Capitalism is a class society, involving a contradictory relation between bourgeois and proletariat. One cannot exist without the other but their interests are opposed. They must fight, just as slaves fought masters and serfs fought lords. Humans arrive at capitalism when they resolve the contradiction between slave/master and serf/lord. (This is very reductive example, as there are many classes in every epoch of class society.)
Humans will arrive at communism when they resolve the contradictions of capitalism. Rosa Luxemburg once said, 'socialism or barbarism', roughly meaning we either head towards communism or we let the liberals/fascists continue their barbarity. (When MLs say, 'liberals', they mean all those in favour of capitalism, as liberalism is the ideology of capitalism; and they become fascists to protect capitalism against revolution.) Now we can add a third, 'or planetary collapse'. We either head towards communism or decide how quickly to destroy the climate. There's no option where it isn't destroyed unless we head towards communism.
But, according to himat, communism isn't the final stage of human development. Because contradiction is in everything. And the struggle between the opposites within those contradictory relations drive change. We're just unable to see exactly what contradictions will arise once we get past capitalism and abolish classes.
I think you might already see things in a similar way, as you identify the germ of the existing system in the Roman system.
And this takes us to e.g. the USSR. I'll try to be brief. It's not that MLs/tankies support the USSR. I'm not even sure what that means as the only kind of support that counts is material support. Although material support can be ideological, there's no USSR in existence to which to offer any support. It dissolved several decades ago. The only thing left is critical analysis of what it was, how it worked, and why it ultimately failed.
Following such an analysis, the evidence takes us to whatever conclusions it takes us. Looking at that evidence to fully understand the USSR, it's clear that it was not what the anti-communist narrative says it was. If this is a more favourable view than we've been taught we're allowed to have, then someone is lying and propagandising and we must ask, why?
We can get into more details about these subjects if you wish, although I may ask others to chip in depending on what you ask. But if you are here in good faith, which seems to be the case, please keep asking questions.