From my own experience and what I've gathered here, entering a Skill Challenge isn't something that the players have control over. It's imposed by the DM, in response to the PCs trying to accomplish a task, where the DM wants to make things complicated. The DM decides that this task carries a certain amount of narrative weight, so the PCs will need to overcome X number of level-appropriate challenges in order for the outcome to be suitably dramatic.
As was explained to me above, the DM might decide that 6 successes are necessary, and then starts allocating those among the various sub-tasks that come up. You need to gather raw materials for that boat? The DM decides to spend a challenge on that in order to invoke uncertainty here; it can be a medium DC or a hard DC, but whatever the DM decides to spend, it will eat up the designated amount of drama budget and reduce the number of further complications might arise.
Declaring a Skill Challenge is a purely antagonistic move by the DM, against the players, via Rule of Drama.
At least, that's what I get out of this conversation.
Well, I think again it's about the upfront work.
If you're using SCs in your game, I would assume your group enjoys dramatic tension in scenes, actually wants to encourage this, and has decided that SC are a helpful tool to this end.
Whether to use a SC or not is often trigger by the DM but I would think the player's should agree it's the right time to use one. And the player's should be looking forward to SCs as well --- after all they should be a fun part of the game as well a resolution tool.
If your group is not in this mindset, why are you using SC? If you approach the concept with this antagonistic mindset, anti-conflict mindset, etc. then of course SC are going to be a bad experience. Don't use them. It's not really the fault of the structure though.
SC do not have to be an antagonistic move -- they can be a solidly collaborative move if the group is on the same page.