There are numerous examples of the police turning up on a suicide call and killing the individual, even when unarmed[2][3]. They simply aren't qualified to deal with suicidal individuals and should only be used when other's safety is at stake.
[0] http://thehill.com/opinion/healthcare/375040-police-need-mor...
[1] https://www.theatlantic.com/national/archive/2014/12/police-...
[2] https://www.thedailybeast.com/unarmed-teen-killed-by-police-...
[3] https://www.mercurynews.com/2017/11/02/santa-clara-da-clears...