If skillbars were unlocked by default, people would complain about skillbars unlocked by default and them losing a skill from the bar. Tricky, isn't it?
Not really, no. Just prevent it from defaulting back to locked once changed. Problem solved.
I don't care about the click from time to time, but I also don't care about achievements (what's the sense of them?) and use a mod since long to avoid items entering my skillbars.
Yeah, I will probably do the same once I finished my first playthrough. I generally prefer to abstain from applying any mods until then. I don't care much about generic achievements either, but sometimes they can be nice as they might point out different ways of how to handle a situation that you might not have realized otherwise. Or hint at some secret places / possibilites / choices. Otherwise I guess they just offer a sense of progression to people akin to the leveling up process itself.