You are greatly exaggerating the direct culpability of the Kaiserreich in bringing the Communists at power in Russia, both in hindsight and in the judgement of 1920s international public opinion. While it was a reckless gambit that exploded in their face, a Russia under Lenin was certainly not what they meant (rather to add a little more internal instability to post-Tsarist Russia adn bring it to the peace table sooner). It's like saying that because Reagan sent support to Afghan mujaedin, America willed, and bears direct culpability, for Al-Quaeda. There is very little evidence that mainstream 1920s public opinion shared your... odd view.
Actually I'm understating it so I don't drag in the few resident Soviet apologists to explain that "No, the Soviets really did have a mass support they never had." The Bolshevik Revolution in October was bought and paid for by the Kaiserreich to get Russia out of the war on the cheap. Long-term thinking didn't exist in Germany then or later. These ties went all the way back to 1915, accelerated as despite the massive losses, overthrow of the Tsar and flip-flopping in terms of Revolutionary-era Government Russia just would. not. quit.
Germany made the Bolsheviks and didn't realize what they'd done. Then Germany repeated the exact same mistake by letting in another attempt by the German military to influence politics, the result of sending political officer Hitler of Branau-am-Inn to the DAP into power. The German military literally created all the horrors of the 20th Century. I understate this again to avoid needless wankery about this but since you happily offered the chance for me to point this out.....
I meant a Weimar Germany with 1938 borders (plus West Prussia and Memel), a reasonable amount of reparations, and sufficient rearmament to protect themselves from the Reds since the 1920s would have no real reason to hate the Entente or plot another war against them.
Why are the Allies going to let Germany do this instead of doing it themselves if they're this willing to slog into Russia?
And the ToV crap was still in place. Big deal.
Sevres, St. Germain, and Trianon expose the degree to which 1920s Germany was full of treacherous, whiny little bitches at the highest levels and fascist scum on the fringes who didn't appreciate what a bunch of mealy-mouthed whiny supercilious slippery lying douchebags were running the Weimar-era Republic. Germany was not forcibly dismembered like Hungary, nor was it intended to be altogether erased like the Ottoman Empire. The Germans, however, had not the memory or ability to think of goldfishes at the highest levels. If they had had such ability it would have been immediately obvious to them that Versailles actually strengthened Germany, not weakened it, by leaving it mostly intact and its enemies all the legacies of having to rebuild from the territory fought over to the degree it resembled Mordor. They would have thus assured precisely the kind of peaceful path to hegemony you're talking about while leaving Versailles intact and eschewing the self-contradictory rearmament program followed by Hitler's wretched hive of scum and villainy.
Instead they just decided to go give the Soviets the starting ground for the very army that would later take over a good-sized chunk of Eastern Europe.
If the immediate aftershock of the Soviets in Warsaw means Germany gets the Entente-panicked goodwill to negotiate its way out of the ToV crap, that is going to stand as the new, much more stable status quo in German-Entente relations, even later years show the Soviets did not really meant an all-out bid to conquer Europe in the 1920s.
Again, the Allies went to war to sustain Sevres. A Soviet victory at Warsaw that doesn't go anywhere, which a realistic victory will not, will not lead the Allies to in turn start creating Germany anew as a military power. 1921 is not 1946, the USSR is not a military superpower ruling half the continent.
That's an exaggeration. They would self-destruct if they pick a fight with one or more of the European great powers, which isn't guaranteed to happen till they violate the German or Italian space or invade Greece or Turkey.
If the Poles collapse and the Soviets reach Warsaw, Poland shall simply become another major non-Russian SSR like Ukraine, and the Baltics and Hungary would more or less fall in their lap by themselves. Butterflies can go in various different directions, but the rest of Eastern Europe would find itself in a very precarious situation, without any need for an overwhelming Soviet effort.
Given the degree to which France and the UK were already getting involved a second time in the Polish-Soviet War as they had been in the earlier phase of the war, the Soviets deciding to push on and risk the same fate that claimed the Romanovs and Kerensky only happens if they're driven by the same suicidal impulses that animated WWII-era Japan and Germany. They were not and never were this, otherwise their whole orientation in politics would be very, very different.
Why is Hungary going to go Soviet after defeating its own Communist Uprising? Again, 1921 is not 1944. The USSR's arms have no prestige. The kind of narrow victory a full-scale defeat of Poland requires deprives them of the ability to press on afterward without leaving the risk of Wrangel controlling the Crimea and thereby assuring the Soviets face a permanent Vendee denying them access to the Black Sea. Soviet leaders could read maps, they knew as much as the Allies did the risk of a permanently hostile Crimea.