However CotGP is not a description of communism, but a criticism of Lassalle.
It’s a criticism of Lassalle that also contains a description of communism. These things aren’t mutually exclusive.
Since we can’t possibly imagine what those experiences will be in “communist society” we can’t imagine a communist individual existing in that society.
Marx violates this in TGI.
The issue you seem to be having throughout everything is the comprehension of revolutionary subjects as unconscious pseudo-subjects, where revolution comes about as a mechanical inevitability springing from capitalism, and ““communist society”” (unpredictably) from this (“communist society will be brought about”), hence the ability to preserve the movement towards communist society via ~“revolutionary praxis” but do away with this as the ultimate goal.
So communism isn’t actually defined by a future condition but by a present condition that will continually develop into the central characteristic of individuals in communist society.
For Marx, communism is defined by a present condition (“the premises now in existence” ~ TGI) which carries the possibility for the creation of a communist society (“Looked at historically this inversion appears as the point of entry necessary in order to enforce, at the expense of the majority, the creation of wealth as such, i.e. the ruthless productive powers of social labour, which alone can form the material basis for a free human society.” – Draft Ch. 6 of Capital). This possibility is immanent to these conditions and therefore Marx and Engels can sketch certain features of this possible society through studying present society and its historical premises, which is the actual basis for their call for the proletariat to become organized and unite.
I don’t care if you disagree with Marx but that is what you’re doing.
Ideas only exist in practice.
This isn’t what Marx is saying, nor is it true.
This is a total dismissal of the definition of communism as some future idyllic society. Right here at the beginning of part two of the manifesto.
I already addressed a very similar passage from TGI.
If imagining a better world is the impetus for actually engaging in the here and now, then that’s a subjective factor that is part of the process.
No, it's absolutely not just motivation. Communist society being a real possibility/historical necessity (in what is effectively though not explicitly a moral “should”), is what Marxism rests on–this is where “historical materialism” is supposed to transcend the “social materialism” of classical political economy. You can’t justify the call for global proletarian revolution without this. If it turns out that Marx doesn’t manage to prove this, that it can’t be proven because of when the owl of Minerva spreads its wings, then the only thing to do is to drop Marxism.