The people advocating defunding the police literally believe they can be replaced with on site social workers and therapists. This comes from a viewpoint where crime is simply the product of racism, poverty, or whatever. So a talk down by a trained therapist in their minds will somehow prevent crime from happening.
While having psychologically trained staff can probably be useful in some situations-domestic disputes, autistic or mentally ill people harming themselves or others, abusive families, etc... in your general robbery/mugging/gang murder they are absolutely useless. Unless they have magic empathy/persuasion powers which the people advocating defunding the police seem to believe.
They reference Europe as a model...when not even Europe is this "soft". Police in Europe will shoot if they must. They generally rely more on the threat of force to get criminals to comply, though they can definitely wrestle suspects to the ground too.
Its a combination of naivety and patronization honestly. It assumes a gentle social worker with a masters in interpersonal conflict psychology will get a gangbanger to stop committing a crime in progress, while also assuming said gangbanger isn't really responsible for his actions. Racism, poverty, poor education, xyz are and that he can't choose to you know not be a gangbanger.
Its an extremely stupid sort of "thinking".