Mao wasn't supportive of the United Front for most of the time it existed. The Comintern had to drag him into it and he still kept sending urgent letters about how they needed to break with the KMT. The South Anhui Incident happened after Mao repeatedly warned about it. Mao and Enlai never fully got over what happened, and it wasn't just humiliation at the hands of the KMT, but at the fact that they had to obey the Comintern even when they felt that their mentality was still correct.

People tend to over sell the willingness to collaborate in a united front, but there is a decent amount of evidence that Mao was ready to kill Chiang in the Xi'an incident. According to Edgar Snow Mao was enraged at the order to let him go, and Enlai implies that it was out of discipline that they listened, not that they agreed (Snow's Private Notes on China pg 1-3 and Wu, The Sian Incident pg 101). But regardless, when the KMT did shit that was fascistic or collaborationist, you know what the CPC did? they fucking FOUGHT them. They did not maintain the alliance no matter what, they didn't simply play the long game like you want to imagine. They had lines and when those lines got crossed, they pushed back HARD.

When the KMT ordered both Communist armies to fall back to pre united front borders and surrender. Mao was requesting being allowed to do a preemptive strike as of November 7th 1940. Chiang assembled 200 thousand troops to invade CPC territory in preparation for an expedition if the 4th and 8th armies did not shrink and leave the front lines.

Mao then sent this in Jan of 1941 after the fight broke out

In accordance with an order by Chiang Kai-shek, our Fourth Army, numbering over ten thousand men under the command of General [Chen Yi?],258 is moving north from the southern Yangzi River region but was surrounded by a ring of seventy thousand troops sent by Chiang Kai-shek. Bloody fighting by both sides has been under way for eight days and nights. In the northwest more than three hundred thousand troops are already concentrated, surrounding the border region of Shanxi-Gansu-Ningxia, around which have been erected military blockade installations stretching for several thousand versts.259 The danger exists that our army will be completely destroyed. Simultaneously Chiang Kai-shek has sent more than twenty divisions, which have deployed in a broad offensive against our partisan army bases in four provinces: Jiangsu, Shandong, Anhui, and Hubei. They are preparing mass arrests and mass murder on a China-wide scale. The reactionary atmosphere is extremely serious. We are preparing in political and military terms to direct an energetic counteroffensive against such a broad offensive as is being waged by Chiang Kai-shek.

Even Dimitrov agreed with Mao's stance here after having said to avoid a rupture on Jan 4th, writing to Stalin that the United Front cannot exist under those conditions and concessions to Chiang must be halted until he acquiesces

No matter how grave and perilous the position of the Chinese Communists, they cannot let the criminal attack on the Fourth Army go unanswered and cannot fail to defend themselves against the armies of Chiang Kai-shek now attacking the Eighth Army and the Special Region. Thus, if Chiang Kai-shek does not suspend the aggressive actions being taken by his generals, large-scale internal, internecine war will inevitably flare up, which, of course, could only favor the Japanese. In the interests of avoiding such an internecine war, alongside possible means of influencing Chiang Kai-shek through the Soviet network, the appropriate campaign should be undertaken in America, England, and other countries that would be able to exert a certain pressure on the Chinese government and to a certain degree influence Chinese public opinion. I submit that that campaign ought to be conducted through two avenues:

1. By exposing the criminal actions of the Chinese reactionaries, who are disrupting the unity of the Chinese people in its struggle against the Japanese invaders, in the foreign, China-sympathizing press.
2. By directing protests to Chiang Kai-shek from friends of the Chinese people (various societies, organizations, prominent public figures) and appeals to him and to the Chinese people not to allow the unleashing of internecine war and a schism in the united anti-Japanese front, not to allow the Japanese to conquer China “by the hands of the Chinese themselves.” We can communicate instructions on organizing that campaign to our comrades through entirely secure channels.

Mao refusing to stand down, and essentially causing a break in the United Front by standing firm led to the KMT having to give up, save face, and embarrass itself as the response from everyone including the US per Roosevelts direct pressure was that Chiang was in the wrong. Mao did not simply play the long game and turn the other cheek like you are implying, the takeaway here is NOT that communists should go with the flow.

The Communist won the civil war in no small part because they gained overwhelming support from the populace after events like the South Anhui Incident. You are a fool if you think it is moralizing to say genocide is a line in the sand. If you were actually biased by the history of the Chinese Revolution you would see these examples of the Communists standing their ground and not putting adherence to a united front over what was the correct political and strategic line.

But even if none of this nuance existed that you are just overlooking and painting the Chinese perspective as a singular thing, that would still not change the fact that you are comparing combatting an active invasion alongside fellow countrymen with supporting genocide. You are talking about collaborating not just with people you hate, but with a holocaust as it happens. You are not the brilliant Chinese communist making the tough call in 1937, no you are a fool defending the outright slaughter of Palestinians and collaboration with fascist genocidaires. You are not Enlai, you are a fucking Iron Front member.

Again, enjoy the blood bath, plenty of time to think about the long haul while the corpses pile up around you. fascist fuck