I have a private theory, for which I have absolutely 0 evidence, that the forces of the establishment have some way of sneaking stupid unpopular things or phrases into the left’s discourse which the left then seizes and runs with, much to the establishments’s delight. E.g. renaming the Green Party the Green-Rainbow Party, climate activists attacking famous artworks, things like that.
I have 0 evidence for this, as applied to “defund the police” or anything else. Actually I sort of suspect that “defund the police” was an original creation of the ACAB contingent which meant exactly what it sounds like, that got retconned by more sensible but still reform-minded people into meaning “more properly fund everything else” for exactly the reasons we’re discussing. But as a general rule I suspect (again, with 0 evidence) that some of what you’re talking about actually comes from deliberate sabotage.