Hedonism is a school of thought that argues that pleasure is the only intrinsic good. In very simple terms, a hedonist strives to maximize net pleasure, in some cases without regards to conventional ethics.
Ethical hedonism is the idea that all people have the right to do everything within their honorable power to achieve the greatest amount of pleasure possible to them. It is also the idea that every person's pleasure should far surpass their amount of "pain" (SM likely being considered a form of pleasure in this case).
It is argued that if social constructionism is going to come to grips with morality and agency it must abandon explanations that invoke the necessary causation of metaphysical abstractions such as hedonism.