That's exactly the problem. If you "just follow the logic" you can miss important details or edge cases that you would be forced to deal with by coding it yourself.
I wouldn't mind using something like this for mundane tasks, but I would be very careful with these tools while developing high performance code intended to run on specific hardware.
If I'm reading code, I can give 100% of my attention to the logic and details and edge cases, so I'm more likely to pick them up.
While as I'm writing, I'm busy doing all of the stuff that writing code involves, so I'm more distracted and more likely to make mistakes.
This gets proved to me time and time again when I run something for the first time and have to debug it. I look at the offending line, and think -- how could I have made a mistake so obvious that it's immediately apparent? Well, because I was busy/distracted thinking of 20 different things while writing it. But it's immediately obvious when reading it, because it has my full attention now.
Honestly I don't even see how that's possible. Writing code, you're thinking about all the different ways to do it, eliminating the ones that won't work, evaluating the pros and cons of the ones that seem like they'll work, you start writing one and then realize it actually won't work, then start writing it a different way, try to decide what the best approach will be to make sure you're not committing an off-by-one error, and so on...
Whereas when you're reading code for correctness, you're just following the logic that's already there. If it works, it works. How could it possibly take longer than the whole creative process of coming up with it...?
Sure, maybe most people don't read code for correctness well. But then the code they write is surely even worse.