To add to your point, I think of Mao’s fantastic essay On Contradiction: https://www.marxists.org/reference/archive/mao/selected-works/volume-1/mswv1_17.htm

In particular, this part:

For instance, in the period of its first cooperation with the Communist Party, the Kuomintang stood in contradiction to foreign imperialism and was therefore anti-imperialist; on the other hand, it stood in contradiction to the great masses of the people within the country–although in words it promised many benefits to the working people, in fact it gave them little or nothing. In the period when it carried on the anti-Communist war, the Kuomintang collaborated with imperialism and feudalism against the great masses of the people and wiped out all the gains they had won in the revolution, and thereby intensified its contradictions with them. In the present period of the anti-Japanese war, the Kuomintang stands in contradiction to Japanese imperialism and wants co-operation with the Communist Party, without however relaxing its struggle against the Communist Party and the people or its oppression of them. As for the Communist Party, it has always, in every period, stood with the great masses of the people against imperialism and feudalism, but in the present period of the anti-Japanese war, it has adopted a moderate policy towards the Kuomintang and the domestic feudal forces because the Kuomintang has pressed itself in favour of resisting Japan. The above circumstances have resulted now in alliance between the two parties and now in struggle between them, and even during the periods of alliance there has been a complicated state of simultaneous alliance and struggle. If we do not study the particular features of both aspects of the contradiction, we shall fail to understand not only the relations of each party with the other forces, but also the relations between the two parties.

The relevant point being that someone’s, or some entity’s, relation to the cause is not always as simple as “for” or “against”, “helping” or “not helping”, “corrupted” or “pure.” There are times that interests intersect, but are not identical. I’m not sure if it can be generalized adequately how to deal with that fact, but it is something we have to contend with.