Whether they volunteered or not, it is still disrespect. Women voluntarily get abortions - is that not disrespect of life? Others voluntarily submit to euthanasia - is that not also disrespect of life?
The act of consent does not mitigate the disrespect, it only means the consenting person disrespected himself in addition to the disrespect of the exhibitors.
Human corpses as a subject of entertainment is about as disrespectful as can be. It’s not a heck of a lot better than digging up skulls from graveyards and joking “Alas, poor Yorick!”
What it says is that human death is nothing special. That sentiment cannot be separated from saying that human life is nothing special. As I believe in a Creator that is unacceptable to me.
As a Christian, that is my belief. Once our souls have left our bodies, the empty shell means nothing. These are not humans. It is not a disrespect of life because there is no life here anymore! The former occupants of the body have moved on - hopefully to a better place.