I accept that distinction. But what makes you believe volition plays the role you imply (which I assume is that someone who decides something is somehow on a lower moral footing than someone without choice?)
Many people "decide" to join particular religious denominations. Or as we accept more commonly today choose to "identify" as this or that, Do we/should we afford them any less respect?
There's a good argument that a sane and reasonable person who decides something, should have more weight attached to that choice than the person for whom it is a matter of accident.
For example, murder is a more serious crime than manslaughter, precisely because someone pre-meditated rather than killing by accident.
I'm not suggesting you are not dismissing reasonable choice as if it were a lesser thing, just saying it's worth thinking about, because this is not philosophically/ethically clear.
edit:
There's also another quite strong and very different argument, but it's more complex:
There's a line in John Fowles book on the subject of poverty where the protagonist says "Being poor is not something that we are, it's just something that happened to us"
Many identity distinctions are not self-identifications but are imposed by another or group upon someone (or group). For example someone who was a proud Yugoslavian woke up one day with a "Bosnian" passport. Discrimination that come from "other-regarding" sources despite our choices, may feel as egregious as those of accident of birth.