Keep in mind that there are multiple straight paths from the false negative case to the false positive case. I'll give you one examples: pedos can and will use the collider to produce large batches of CSAM that collide with perfectly legitimate images (e.g. common iPhone wallpapers). They literally have nothing to lose by doing this.

Eventually, these photos will make their way into the NCMEC database, and produce a large number of false positives. This will also make the other attacks discussed here easier to execute (e.g. by lowering the human review threshold, since everybody will start with a few strikes).