Yea, I'm one who dislikes labels too except for the most simplistic of concepts and as we all know there's nothing remotely simple about the whole poly equation.
And I often wonder if some of the grabbing at labels isn't just the mechanism some people are trying to use to get some type of handle on this complexity. It's kind of reminiscent of the way people build value systems. In a complex world we need some tool to guide us to make quick, shoot-from-the-hip decisions when we don't have time for a proper analysis.
The "secondary" term I see as being absolutely applicable in SOME situations/times (as Booklady explained) and not in others. The fact that it carries a negative tone is unfortunate - but education CAN overcome that.
It kind of reminds me of a term I've heard a lot - "3rd wheel". Arrgghhhhh
How many times have I heard people say "I'm not being anyone's 3rd wheel" ! Have you guys heard that ? It's so negative ! That 3rd wheel is a critical component of a tricycle !
But in any case - it "seems" to me that the full & equal role of everyone in a relationship is kind of the holy grail that everyone would strive for - IF the conditions permitted. But sometimes they don't and someone plays a "secondary" role. But like the tricycle, that role can be critical and not to be demonized.