The theory is that tasers are a (edit: partial) replacement for firearms for cops. The reality is that approximately 0% of cops are willing to draw a taser if they suspect that someone else has a firearm; they go for their firearm too.
Instead tasers have replaced other methods of de-escalation and containment, which is very bad if you're not a cop. Combine this with cops being called out for people experiencing mental health crises, and this is a recipe for disaster.