Frank Keenan from Biosecurity Queensland contemplated in an email to me that the cat might represent Australia's worst feral mistake. Cane toads are firmly lodged in the national psyche as one of the dumbest moves we've made - introducing them as a biological control almost three quarters of a century ago. However, in discussing the earlier post on TNR, Frank pointed out that cats were seeded to much of the country as a rabbit control measure.
Too much like the lady that swallowed the fly.
I don't think we've ever introduced a third-order pest. One to get rid of one we introduced to get rid of another?