[TeMPOraL]

Nah, if plastic-eating bacteria were released to the wild, it'll be something between a huge annoyance and a civilization-ending disaster. Plastic is a wonder material, and while we definitely don't give it its due respect, it plays crucial role in places like hygiene and energy efficiency. Imagine if you suddenly had to worry about all the plastic things around you rusting.

Also yes, engineered bacteria and viruses are dangerous stuff, but that's the closest we have to a self-replicating robots today. I don't know what else the OP could have meant, besides making a joke. That said, if we change "self-replicating" to "cheap and mass-produced from recycled material", then the whole thing starts to make more sense.