It is the only reproductive strategy of several major diseases, most notably cholera. So yes, obviously it is common. You know how cholera is notorious for spreading through communities very quickly? Guess how that happens.
Intentional consumption of other people's feces is rare, but that's not relevant to anything. If you eat something, it doesn't matter at all whether you wanted to eat it.
The rabbits example is a good one to illustrate it already does happen. :)