Minor but important point: the grey goo scenario isn’t limited to the surface of the earth; while I’m sure such variations exist, the one I’m most familiar with results in the destruction of the entire planet down to the core. Furthermore, it’s not limited to just the Earth, but at that point we’re unlikely to be able to notice much difference. After the earth, the ones who will suffer are the great many sapient species that may exist in the galaxies humans would have been able to reach had we not destroyed ourselves and damned them to oblivion.