Modern computers are ridiculously powerful, processing a 4k image with a 50x50 filter is real time >60hz on cpu using a decent fft solution, and on a decent gpu you could do many times more >60hz.

Oh sure, there are lots of usecases for fast but bad. But what bugs me is that people arent using them for those cases. Worse still, people are using repeated fast but bad, and then more fast and bad to fix the problems that caused, and effectively creating slow and bad filters.