Not a scam that's oldschool, but the scam of the concept of oldschool. Throughout the metal scene, you'll see an obsessive reliance on the oldschool, on canonical works of death, black, or other styles of metal, and even a surprising interchangeability of that term with a supposition of quality. Really, the oldschool scam isn't one thing, but many, and we'll have to look at them all to better prepare you to handle the stupid people around you.
1. Retro = Oldschool
This particular chestnut is perhaps the single concept I would say is the scourge of the metal scene, right now. Yes, modernist genre-fusions and idiotic bids towards mainstream accessibility are all obnoxious, but none of them seem as reductionist and damaging to the integrity of the scene as the retro = oldschool concept. At first, it seems deceptively logical: all these different bands on Razorback are playing oldschool death metal, right? I mean, it seems obvious at first: they're a little bit slower, they're not infused with massive amounts of technicality, and the general execution of the music is designed to mirror the older styles of the genre.
The problem with this whole idea is a pretty big and abstract one: music can never be entirely divorced from the era and sociopolitical climate in which it was made. Take, for example, D.R.I. or any number of oldschool crossover bands: they wrote songs that were a response to Reagan-era conservatism and the society that formed and reacted to that presence. These bands are unique and sound the way they do because this was a certain era in American culture and underground music. Unfortunately, much as many bands would like to believe, Bush is not a replacement for Reagan, and an Xbox is not a replacement for an Atari. Despite similarities to the current era, no single cultural element can be exactly replicated later: context changes, culture changes, and previous concepts are left in the dust.
This is why all attempts on the part of retro-bands to create oldschool metal are doomed to failure. This inevitability does not necessarily mean that bad music will arise; there's plenty of bands I like that play in the retro style, and while the music they make typically doesn't really end up sounding like that era of music, it can be good in its own right. However, for the most part, these bands fail miserably because the emphasis has been taken off making good music and has been placed on replicating an aesthetic which, due to the passing of time, is functionally impossible to replicate. While they might have the best intentions, the fact is that the 'oldschool death metal era' has passed, and no Razorback band is going to recapture its particular magic authentically.
2. Oldschool = Good
This is a pretty simple matter- hindsight is 20/20, but the passage of time also eradicates lesser artists. Looking back, Florida circa 1990 or Norway circa '92 probably seem like perfectly fertile creative landscapes for extreme metal. I mean, look at the early '90s as a whole- many of the formative albums in death and black metal were made during this era, and as such, many look back on these periods with fond memories. However, they also put these eras on a pedestal of sorts because they fail to acknowledge the legion of bands that never made it to the level of Deicide or Darkthrone.
Even a little digging back into these formative years of extreme metal will reveal artists that are mediocre or even terrible, but were simply ignored and eventually forgotten as time passed. Rarely do awful bands without support from the greater musical community survive for long- as such, there's not a whole lot of completely terrible death or black metal bands that began in the late '80s continuing today. It's easy, looking back, to only see the canonical works that many of us have been raised on, and see the era they come from as being this perfect period of creativity. However, like any time in history, there's just as much bad then as there is now- the ratio has simply skewed because there's so many more artists working today and contact with them is much more immediate.
The concept of a classic record (or a classic piece of art in general) is something only established many years after the fact- when it was released, Deicide's 'Legion' was not immediately regarded as the titanic death metal record it is today. As such, there's classics shooting up around us even now, in 2011, which we won't recognize for a very long time. Metal hasn't imploded and lost all artistic relevance- you just haven't been around long enough to see it continue.
3. Oldschool = Savior
This is perhaps the most poisonous ideal of all the oldschool scams, but not for the reasons you're thinking. Many are convinced that the only way metal can survive is by pulling ideas from the golden age of extreme metal and reinterpreting them for a modern obvious. This is impossible because of the first oldschool scam listed above, but the real reason that it's impossible is because people are looking at aesthetics rather than the content which makes oldschool albums so enduring and relevant today. Mayhem's 'De Mysteriis Dom Sathanas' wasn't just in the right place at the right time: there's things going on which make that album endure even today, but those are ignored when it's much easier to just look at blast beats + tremolo riffs + grumbling vocals and call it a day.
Let's look at that album in particular for a moment: what parts of it are so essential? The riffs are incredible, but what about them? Well, for one, they're just as much thrash and traditional heavy metal as they are black metal- there's a ton of melodic and rhythmic variation which keeps them constantly exciting and shifting in tone. The drums are somewhat similar; thrashy and oldschool, but at the same time, there's an intensity to the way Hellhammer composes drum lines, shifting rhythms under riffs in a way that changes the tone of the riffs as well as propels the song forward- it's not something particularly common to black metal, but it for a wonderful black metal drum performance. Then there's the vocals- hell, Attila's vocals don't sound like a traditional black metal scream at all, but a gothic grumble and even operatic wail, which is at once unique and perfectly matches the overall tone of the album.
Do you see the common theme here? Of course- none of the defining elements of this album fall neatly within the lines of 'black metal'. Mayhem were operating without a hard and fast concept of what black metal really was: they had an idea of it and attempted to make that idea come to life, but without preconceived notions of what that was supposed to be. This goes for all the other oldschool records which are so heavily revered today: rarely did they operate cleanly within their genre. Autopsy would mix punk, doom, thrash, and death metal. Morbid Angel would draw influence from Jimi Hendrix but reinterpret him in a new context. Emperor would look to classical music for inspiration, but would change and warp them for use in black metal.
For all people say about metal being an independent form of music, the lines of genre, style, and what one can and can't do within them have been firmly established. The answer is not an arbitrary combination of styles- shoegaze/black metal, funeral doom/post-rock, grindcore/ambient- but a reduction of the influence of style overall. Hellhammer started making music which ended up being the metal we still revere today, and many of the greatest bands out there started the same way: with music as the priority before everything else. I have no doubt that there's a lot of kids with guitars out there reading right now, so if there was one thing I'd like to say to you, it's this: don't try to start a band that's 'death metal' or 'black metal' or whatever you think it should be: just start writing music and let your art find its own voice, whatever that may be.