I sympathize with the man who died in custody. Police brutality is not something we can casually gloss over, but I'm not sure how we can make the police responsible for preserving the life of a man who was effectively committing suicide via gluttony.
If the suspect lacks the instinct of self-preservation, it seems a bit absurd to make law enforcement responsible for keeping him alive.
I guess the day someone kill you, we will say that it was a case of suicide via being an a**hole. This guy likely had at least +15-20 year life expectancy ahead of him, to suggest that the enforcer of the state, have no responsibility for looking at a guy they arrest and think "we better be careful we don't kill him", is blindblowing. What you suggest are that the police should have a right to kill anybody they feel like killing.