What it comes down to is a matter of trust. For example, let's say there's a strike going on and management makes a generous offer, but it would only apply to the senior employees. If the union accepts this, then the newer employees will feel like the union is only working for the people who have been there longer, and are less likely to take risks or stick their necks out for the "common good," because that "common good" seems to benefit some people more than others.

Now, with the workers divided, they have less power and less ability to resist whatever the company decides. In time, even the senior employees may end up worse off.

However, I do agree with you that you don't have to do everything at once. Small victories can serve as a proof of concept, showing tangible results of organization. But there's a difference between a small victory that's shared or fair and a small victory that only benefits part of a coalition and serves essentially as a bribe.

In the hypothetical of "freeing half the slaves" it's kind of impossible to answer from a purely theoretical standpoint, it depends on the specific conditions. If the level of trust and political consciousness is high enough, then the ones who benefit can be trusted to keep fighting for the others and the others won't feel betrayed or left behind. But if it's a fledgling coalition and opportunists are present, then it's a recipe for the whole thing to fall apart.

Every proletarian has been through strikes and has experienced “compromises” with the hated oppressors and exploiters, when the workers have had to return to work either without having achieved anything or else agreeing to only a partial satisfaction of their demands. Every proletarian—as a result of the conditions of the mass struggle and the acute intensification of class antagonisms he lives among—sees the difference between a compromise enforced by objective conditions (such as lack of strike funds, no outside support, starvation and exhaustion)—a compromise which in no way minimises the revolutionary devotion and readiness to carry on the struggle on the part of the workers who have agreed to such a compromise—and, on the other hand, a compromise by traitors who try to ascribe to objective causes their self-interest (strike-breakers also enter into “compromises”!), their cowardice, desire to toady to the capitalists, and readiness to yield to intimidation, sometimes to persuasion, sometimes to sops, and sometimes to flattery from the capitalists.

• Some guy