I think there might be a little confusion about terminology here. "Spinning" and rewriting are not the same thing.
Rewriting an article so that it targets a different audience (for instance, taking a technical report and turning it into a white paper intended for non-technical corporate executives) is totally OK. In content marketing circles this is referred to as "repurposing."
It's a great way to get multiple uses out of the same basic content. After you've made the white paper out of the technical report, you can then take that white paper and break the content up, do a little massaging and you've got several blog posts. Take those blog posts and rework them into slides and you've got the starting point for a webinar. And so on and so forth.
Each piece of content you create is unique, hand-crafted and well suited to both the target audience and the delivery medium. There's absolutely nothing wrong with that -- it fact, it's exactly the sort of thing one should
"Spinning," on the other hand, involves automated software. Basically the site owner feeds in an article, either an original one they wrote themselves, or (more typically) a non-original article they either downloaded from an article repository or "scraped" from another legitimate website.
They then feed the software a lists of alternate keywords. The software then "slices and dices" the article, inserting synonym keywords and rearranging the sentence or paragraph order to create what the software authors call "unique content."
In the classic form of spinning, the site owner can easily create hundreds or even thousands of articles in a matter of seconds.
Now, most of the articles read like crap and are of very low value, but that's not the point. The site owner then posts these (also using automated software) to thousands of made-for-Adsense (MFA) blogs.
The idea is that when visitors land on these pages, the articles will be crappy, but the contextual ads will be relevant to the keywords on the page. With luck, visitors will bail on the article and click one of the ads instead, still trying to find the information they were seeking. The site owner then pockets the money from the click.
Each page is completely worthless. Some pages may only get one or two visitors, ever. Many of the pages will never generate a click at all. But with literally millions of pages "spun" out there, even a small percentage generating clicks can make money for the site owner.
Google has tried to crack down on this. That's one of the things the Panda update was designed to do. So it's made it harder, but not impossible, for this scheme to work. This is a good thing, but (speaking as a professional writer) I'd be even happier if they'd find a way to eliminate it entirely.
The problem is that some site owners who aren't in the spammy MFA arena have fallen for the marketing of the "spinner" software sellers. When selling this software, they tell site owners that they can use this software to create "unique" content for the site owners' blogs (nudge, nudge, wink, wink).
The real MFA crowd knows exactly what they mean and exactly what the software does (see above), but some innocent site owners are fooled into thinking this is a good way to create additional content for their legitimate websites, mistakenly believing "more" is the same as "better."
There is nothing wrong with rewriting/repurposing content. There is a great deal wrong with "spinning."