So, if you do almost no real-world testing, and rely on theory and shapes largely derived from the 1930s, it's possible to develop a very odd idea of what is actually going on.
Then, if your first premise is utterly wrong, you are potentially in a position where you build upon that faulty foundation and come up with a second premise, that is equally wrong. And so on...
First faulty premise: if the shape curves downwards faster than The Template, flow separation will occur.
Second faulty premise: if the shape curves downwards faster than The Template, flow separation will occur
and therefore low pressures - and so lift - are due to separation.
Then, if you are completely seduced by your weird theory, you can extrapolate it into absurdities - a third faulty premise.
Third faulty premise: rear spoilers reduce lift by 'reaching up' to the streamline that would have occurred had 'The Template shape premise' (ie Premise 1) been true.
(To be fair, the third faulty premise is faulty only on cars with attached flow. Where separation occurred at the end of (say) the roof on a sedan of the 1960s, this was a valid idea [just not with The Template as the demarcator] and certainly not with cars of the last 30-odd years.)
The we add to the mix:
- a believer in these faulty premises who sometimes writes in an incomprehensible (but impressive-sounding) pseudo-technical English
- a largely uncritical audience that doesn't know much at all about the subject (sorry, guys)
- something I have noticed that dominates discussion groups with largely US contributors, and that is a really strong peer pressure to not call out rubbish being spouted by others (it's apparently seen as being rude)
.... and so we end up having completely invalid notions being accepted, regurgitated and defended.
One of my undergraduate majors was sociology. I sometimes think I should do a doctoral dissertation on hobby-technical BS spread by discussion groups...