I think it's on the assumption that this team won't be ready to "compete" for another 2-5 years. And in terms of sustainability, it's in the team's best interest to find a PG who will be in his prime during these years, not the twilight of his career. I don't know if people want Calderon gone per se, but instead acknowledge the fact that he's not our long-term answer.
What to do with him is anyone's guess, whether you trade him, let his contract expire, or re-sign him as a backup PG.
You nailed it.
If he stayed healthy that would change things but I see the risk too large.
Regardless, another wing is the more pressing need at this time.