The single objective bias occurs in some win-win measures: someone who advocates a win-win measure because of one objective has a single objective bias when s/he strongly criticizes other people who have different objectives but promote the same win-win measure. This criticism might undermine the efficiency of advocating for the measure and hence might impede the objective one holds dear.
Perhaps the most important win-win measures are: veganism, family planning and tax shifts. In all these cases, there are people with certain objectives who criticize other people for having the wrong objectives even though those other people promote the same measures.
Regarding veganism, some animal rights activists invest a lot of time and energy criticizing other people who are vegan or want to become vegan due to health or environmental reasons. The animal rights activists think that the health and environmental vegans have the wrong objectives and some even believe that advocating veganism for health and environmental reasons is counterproductive. They believe that you should always refer to the animal rights objective when promoting veganism.
Regarding family planning, some feminist activists criticize environmentalists who address overpopulation and promote family planning to solve the problem of overpopulation. Those feminists believe that the single objective of family planning should be women’s rights. They often believe that promoting family planning because of ecological sustainability is disrespectful towards women.
Regarding tax shifts, some libertarian socialists (left-libertarians) argue that the objective of a tax shift away from labor tax should be worker’s rights: the right to own the products of your own labor. They criticize environmentalists who promote the same tax shift (from a tax on labor to a tax on natural resources) for the sake of environmental objectives. They criticize economists who promote the same tax shift because of economic efficiency objectives. As if worker’s rights should be the single objective.
It is as if those animal, women’s and worker’s rights activists are not willing to accept that their measures have multiple benefits beside their own rights objectives. Their own objectives might be reached more efficiently if they embrace the efforts of other people (the health devotees, environmentalists, economists) who promote the same measures with different objectives.