Incidentally, how does a slave trust her master with her life?
I will tell you how very simply, a slave allows the Master to make all decisions for her (save the one... stay or leave) and therefore in essence she is giving him her life or "devoting her life" to him in a very real way. And, it is one of his responsibilities (again, our level of responsibility seems to differ but by your own definitions you do seem to agree that a Master does make all the decisions and there is little room for negotiation and that in itself is a HUGE responsibility) to protect that life that she has basicly given him. She trusts him with all of the decisions in her life so therefore she trusts him with her life. Also, in extreme BDSM (which is not the norm but still exists), a slave does literally trusts her Master with her life quite literally as she trusts that he is going to keep her safe and unharmed through his knowledge, skill, wisdom and commitment towards her life, her well being and her growth. Again, I don't see Dominants having that level of commitment. Sure, they are going to keep things safe/sane/consentual but are they going to care about the slave's long term growth, well being and life in general? I don't believe the average Dominant is very concerned with these things but a Master will (or should be) concerned about these things.