The slogan caters to both sides. When campaigning to extremists, it's a dog whistle and means exactly what the words mean (defund or "abolish" police by virtue of removing their funding). Simultaneously, it's also "oh it just means defund, not unfund" for the tame and middle-ground activists that see problems in over-funded policing as well as for the apologists that want to legitimize the extreme "unfund" part of the movement.

The problem at it's core is that politicians (including activists) and their platforms are not held accountable and their words are meaningless because they have no definition. Like just look at this thread. "Unfund" vs "Defund". How on earth are we supposed to infer that specific meaning and trust the other side to do so as well? It's like a recipe specifically designed for conflict and misunderstanding. Also a perfect recipe for back and forth definition debates like this one, instead of arguing about the core issues.