One of the most discussed and most sophisticated versions of modern rule-consequentialism is Brad Hooker's concept. He blends not only consequentialist but also some intuitionist aspects into a seemingly coherent moral theory. Among many others, one of the main arguments he uses for a variety of purposes is the concept of internalization costs - psychological expenses connected with the acceptance of some code in moral agents (demands on memory, intelligence, inter-personal bonds, etc.). However, at the same time Hooker also insists on just one common moral domain for every moral agent. Therefore an overwhelming majority of everyone, everywhere and in each future generation should follow the same moral code.
The main aim of this thesis is to show that this single-domain structure is highly implausible (if not impossible), when agents involved have relevant differences in internalization costs for some code. Firstly some main aspects of Hooker's theory will be sketched, and then two main series of objections against the single moral domain will be raised: hard-lock problems (technological or genetic differences in internalization costs) and soft-lock problems (external, learned or institutionalized differences). If Hooker wants to avoid these objections, many contingent and questionable amendments have to be invoked, which radically reduce the appeal of his initial concept. As a conclusion it is suggested that one does not really need the single-domain structure in almost any cases, and most of the objections to rule-consequentialism might be avoided without invoking such concept. It is then proposed that Hooker's theory might fared significantly better if multiple moral domains would be allowed. More so, the boundaries and size of these domains could be based on the rule-consequentialist grounds themselves, in order to avoid the feared relativization of moral code to individuals
