Counter-point: AFAIK "fecal matter contamination" usually means "we found some ecoli". A bacteria that is completely ubiquitous and almost always harmless unless you manage to ingest a significant amount or rub them into your eyes. It can be a useful general cleanliness indicator, for example if high concentrations of ecoli are measured in a body of water it probably means raw sewage made its way there, and you should be worried about the things that aren't ecoli. However you're not particularly likely to catch cholera or dysentery from your own sponge.

Furthermore sponges aren't meant to be clean per se. They're meant to be mechanically abrasive, so that all the impurities are detached from the surface you're cleaning. Those impurities then bind to the soap molecules which prevent them from clinging to surfaces, and therefore allow them to be easily washed away when rinsing.
It does not matter much if the sponge was dirty because the bacteria from the sponge will rinse away alongside the bacteria from the item you're cleaning. Just make sure to soap, rinse, and dry things properly and wash your hands after handling a sponge.

Do not look into bathrooms and tooth brushes then.

I change my dish sponge every couple weeks, and toss any that are visibly dirty at all. If it sits in the sink longer than like 20 seconds, trash. I do not understand why people hold on to these $2 items until they're entirely new colors, probably harboring germ colonies on the verge of space travel.