One concept of the step-by-step method of "selling compassion":
"while there is a deep philosophical gulf between animal welfare and animal rights, psychologically and politically there is a continuum. That means on the one hand that it is at least possible, if not probable, that a person develops psychologically from animal use via animal welfare to animal rights. And secondly it proves that it is at least possible – even if we haven’t provided data of its likelihood yet – that a society develops politically from animal usage via animal welfare to animal rights. [...]from: Abolitionism versus Reformism
"Can animal industries be made to completely disappear by step for step victories, which bring incremental reforms?
"From a purely theoretical point of view, the psychological-political continuity from animal use via animal welfare to animal rights suggests that indeed it is possible. A society without any restrictions on animal use sees non-human animals as commodities for the benefit of humankind without any ethical value. Such a society will not have any empathy and compassion for animals. The historic example of Austria before the first animal laws serves as a good example of such a society.
"Historically, from that starting point, slowly compassion, animal welfare and animal laws developed. At this stage, ethical vegetarianism could get a foothold at the end of the 19th century. Slowly, the first ideas of animal rights developed and from the 1980s onwards, there is a lively and thriving animal rights movement. The ideology of animal rights and the animal rights movement have their psychological and political roots in animal welfare.
"Similarly, the development of single people generally advances from compassion and animal welfare feelings, which might have led to less consumption of animal products (probably rather of the free range variety), to vegetarianism and eventually to the full animal rights vision and veganism. Psychologically, compassion and animal welfare form the basis for animal rights too."