All too often arguments against this interpret 'defund' at the farthest possible extreme, but no one is calling for an end of law enforcement.
The reality is that providing constant budget increases for better weapons, faster cars, additional staff, etc. is causing the police to become more militarized. The Military are a defense against enemies. As police become more militarized their enemy becomes the civilians who they are meant to protect and serve.
The actual idea is to defund police departments as they are structured today, and allocate that money instead to social and mental health programs as well as law enforcement with a foundation in de-escalation and transparency.
Of course there would still be law enforcement to maintain peace and safety, and it would be based on transparency and accountability.