Nobody will fire you if you do your job 80% right in 20% of the time. That's because that still leaves me with the other 80% time - which I can do to perform more 80% tasks for a total of 400%. Which the article mentions as the first course of action on what to do with your saved time.
If I write four programs that each are only 80% complete, it's as good as I hadn't written a single one, as they won't be working with just 80% done.
Lots of people have "almost finished" works, but those are still stalled in life because nobody ever finished the remaining 20%.
Lastly, that remaining 20% still has to be done indeed. But humans do not exist in vacuum. Someone else on the project can take care of it - someone who is better with the remaining part than you are, and who has plenty of free time now because you did the 80% for them.
Humans don't exist in a vacuum indeed, but if it's your job to do X, then you're expected to do 100% of X. And other people on your project surely have their duties. If you're throwing your work at them and still geting fully paid at it, you're sucking them of their effort for nothing in return. I'll admit it's highly profitable for you, but I believe most people would consider than unethical at best.
If you do offer them something in return (like take care of jobs they don't like and you do), then you're piling extra work on yourself and you're not just doing 80% anymore.
And if that 80% is the easy part that everyone would like to focus on while the remaining 20% is the hard one and nobody's willing to invest the effort in it - then the 80% wasn't really eighty percent, was it? Just because it seemed like the bulk of work doesn't mean it was.
Thing is, a lot of people will be easily misguided in that department. A project may look "80% done", and then problems start appearing out of nowhere and you need to extend deadlines or work extra hours.
If the person who started the project meanwhile ditched you "because it was already 80% done", then you're in for a world of hurt because of them being a smartass, as you need to go back and review (it not redo) everything that had been done until then.
That's why works have assignments. If you think the workload could be better divided among the workers then discuss it with your boss. But if you go around claiming you did four projects in the time of one when you only pulled it off was by draining the time of four other poor smucks that got fooled by your sweet talks, you don't really have anything to be proud off.
The only problem here is if you leave the fact that this 20% still has to be done unnoticed. Others may assume you're 100% finished already, so good communication is key.
What if you aren't good at communications? The article specifically says to don't waste time with your weak points. Would this mean that "gasp" you have to put some actual hard effort here and there like talking with that coworker you personally dislike?
This is a good article, you have to just approach it from an understanding point of view. Our brains have been culturally hard-wired to automatically reject it, so of course the "my car/power plant/shoes gonna explode!" argument found many supporters - despite being totally out of place, an illogical strawman.
In a more personal scale, I've seen plenty of people geting screwed because their medics decided to just do 80% of the treatments and examinations they were suposed to do. That would allow them to see more clients and cash in more, at the cost of leting plenty of problems slip by and get worst. And then if you tried to bring other medic in to fill the missing 20%, they would have to start almost from scratch because the 80% job done would be mostly irrelevant now that the problems had time to fester (if they had been correctly diagonized to begin with, doing just 80% of your work is funny like that).
Civilian construction is filled with this, only 80% of the budget for the building, and the remaining 20% cashed in for the builder's pockets. Nevermind that the building now has common water and energy shortages and isn't properly isolated because they used second-grade materials to save the 20%.
And let's not talk about one handy men my grandmother hired for her home that wanted to actually charge more than the tabled price if she wanted him to actualy do 100% of the work, instead of some 80% quality patchjob.
So no, it's not wrong that our culture "hard-wires" us in doing our jobs (which we're being paid to do BTW). Because plenty of tasks are unpleasant and boring, but they still need to get done for society to work and advance.