I am very happy with my primary partner; but do hope someday to have multiple primaries.
He and I honestly have no interest in bringing anyone into our poly group who doesn't want a primary style relationship (i.e. wants to be part of our family and build a life together). What that means for the individual relationships varies, but, ultimately, everyone is living and creating together. And, of course, those relationships start out as secondary, or less committed.
As long as you don't restrict anyone's ability to further a relationship, romantically or sexually (safe sex is an acceptable restriction), I don't think there is anything unethical about having primaries/secondaries.