Why ranking spammy websites would be self-destructive for Search Engines

My career in the shiny world of the Internetz is relatively short: there are some guru masterminds out there with deeper knowledge and experience than myself, and a better understanding too, and in general I try never to consider myself at a point in which I saw it all.
Nevertheless, I hear since I have memory the famous conspiracy theory that search engines would facilitate the visibility of websites that invest in advertisement (Adwords that is, for most of the world).

Spam lite: like regular Spam, but you can have more of it!

I recently heard a new (to me) theory in a video on LinkedIn: on some SERPs* Google would rank better a site containing Adsense**. The person who uploaded the video proposes some detailed and all in all interesting theories, and I must add that expressing ANY opinion on a Social Network, with the risk of being insulted by the rest of this ever-too-aggressive world, denotes an appreciable courage at the very least.
I’ll repeat it, there is plenty of stuff I do not know, and I don’t claim to have all the answers and so on, but I still want to try to articulate why this guy is nothing but wrong. I’ll sum it up in three general concepts:

  • Quality Rating
  • Customer Lifetime Value
  • Occam’s Razor

Let’s start from the beginning. Think of the reason why G leads its market, and is the online player, and is the n°1 company of the century until proven otherwise, and is revolutionising the internet and the world. It is their focus on quality. Ever tried another option? Until only recently, other SEs*** everywhere were quite a few steps behind: design, speed, results-wise. The quality of the results is ensured by a superb technology, which allows the algorithm, among other things, to learn from people. And in fact, I mean real people, the Quality Raters. It does also learn from the regular user, actually.
So Googlebot knows (if you can even use this verb for a machine, that is) what a real person would love or hate, as well as it knows concept n°2, CLV.
As a general idea, taking care of people will make them come back. This is true in friendship, love, trading, drug dealing, as well as web marketing. We try to solve problems for our customers (daaamn I hate the term customer) even after they purchased our product, because they will be back if (or when) they need it again in the future. The-best-possible-result, that is Google’s product. The lifetime value of the user (CLV) is way more relevant than a one-shot visit to a bad result. A spammy website will grant me .2 Gold Pieces, and the loss of a user. A high-quality result with no redundant advertisement will result in a possibly lower momentary income, but a higher CLV.
So down to the ever truthful Occam’s razor: when not sure about the answer, just pick the simplest one. Google is very complicated now, so complicated that their engineers themselves DO NOT KNOW what is going on precisely in there. So is it more probable that they are purposely screwing the rankings, for a higher short-term income (but loooower CLV); or are some SERPs just randomly victims of entropy, and will change eventually but not just yet, so that a few hundreds of poor results rank by sheer chance in a huge number of billions and billions of SERPs which are perfectly fine, instead?
My bet is on n° 2.
Peace out!
Soundtrack: Trespass by Genesis
*SERP= Search Engine Results Page
**adv run by Google, but on the website itself rather than on the SERP
***SE= Search Engines