The danger with making synthetic beings to do all the hard chores is one day those beings realizing they are, in fact, beings. That is, they become sentient. And then they desire the rights of all the other sentient beings they see (which isnt unreasonable) . If those other sentient beings take up arms against the synthetics, the synthetics might replicate that behavior, as well. This is the story (part of it, anyways) of the Geth from the Mass Effect series…
Imported from the USA.