If you think about it, Izanami cannot force their victim into an ultimate death or a certain fate waiting for them. What it means to accept fate is to accept fate that has already happened. Escaping a death sentence is not the same case of fate in this case.
In my thinking, the Uchiha clan would abuse Izanagi to avoid death that was already inflicted upon them. Say their arm was cut off, they would use Izanagi to make it as if it never happened. Izanagi makes the impossible possible, and when the victim accepts that impossibility is impossible, he/she will break free from it, thus accepting fate.
So if Izanagi is used to teleport somewhere, in reality is impossible, or avoid death, which again is impossible, and when Izanami is used, the victim has to personally accept that which is impossible cannot be possible. In a sense it is a powerful genjutsu that forces its victim's mind into accepting reality if the victim chooses to succumb. I doubt the user can force the user to accept whatever the user wishes, in which is a one-hit-kill no matter what.
The user must tell the victim what he/she must accept in order to escape the jutsu. This is where the jutsu sets the "safety word" for the jutsu. Izanami cannot force a victim into death but it rather used to give a disability towards the victim. The acceptance stated in Izanami is physical reality and personal truth. It is not a form of brainwashing, but acceptance.
