Advertising can be controlled, and the US is more the exception rather than the rule.
the only parties
Because of first past the post. Ranked choice would help greatly.
two far-right parties
Ranked choice would help. But do you think a large majority of voters are significantly further left than the DNC? Really?
I think the average opinion is between the two parties. So a socialist revolution would be against a democratic consensus. That means you wouldn’t be able to set up a democracy post revolution, because it would be unpopular.
Plus getting rid of the checks and balances is really dangerous in letting people like Stallin, Mau, or Kim Il weasel their way into power and consolidate it to stay there.