What if you don't know whether a thing is worth doing, and the cheapest way to find out is to half-arse it and then with the additional evidence evaluate whether it'd be worth doing well?
On reflection my gripe with the post is really about vocabulary.
Half-arsing carries negative connotations - to me, at least, it is the 'bad' form of pragmatism, and as such in my book it is never defensible.
IMO we have other words to describe the scenario where an expert consciously makes a 'good' or reasonable trade-off to complete a task in a smaller window of time, and should use those instead.
Perhaps reasonable in projects/tasks that you have full ownership of and intend to continue to do so for the foreseeable future. In general though, I think there's good reason to strongly prefer the 'if a thing is worth doing, it's worth doing well' side of the spectrum.