M.D. Brain death is not about a definition of death, although it is often stated as a matter of definition. Rather, brain death vs. death is about the facts of death. One ought to begin with the known.
Death is a fact.
The concept of death can be defined, often from a theological or philosophical viewpoint. The law should be for all. The purpose of the law should be for the protection of citizens. In the case of death the law should protect a citizen from being determined or pronounced dead before death, the fact, has occurred. This is not occurring in brain death.