I suspect we're taking at cross purposes, so I'll try to clarify what I'm seeing.
ZeConster believes that since shadowrunners (each one individually powerfully magical, highly skilled, and/or with gear, implanted or not, valued above a hundred thousand nuyen) are presumed in-game to start out without a SIN, they by default most likely never had one.
Namikaze agrees that shadowrunners start the game without a SIN by default, unless they take the Negative Quality. He doesn't care about what happened before game start, and claims it to be irrelevant.
Lethal Joke is claiming ... not sure. That shadowrunners start the game without a SIN by default, unless they take the Negative Quality. I think.
All right. I never claimed that shadowrunners defaulted to starting the game with a SIN; I agree that they by default start without one, unless they take the Negative Quality. This has never been in question.
My debate with ZeConster is what Namikaze claims is irrelevant - but which is exactly why this thread started, to wit "Can I RP out a character getting a SIN burned, so he can buy off the Negative Quality of having one?" My answer was 'yes', and that most other characters who had not been second-generation runners or born and grew up in the Barrens are assumed to have done this, so what SlowDeck is simply playing out something that many, if not most, characters have already undergone.
So the issue lies in 'where do most shadowrunners come from?' Not in whether or not 'most shadowrunners' start the game with or without a SIN; clearly, to start with a legal SIN one must take a Negative Quality.
My position is that out of the 7 billion people on the planet, and the 3+ million people in the Seattle Metroplex, most of them - 6.8 million at least in Seattle, unless you think that more than 200,000 or so people live in the Barrens, equating to 3% of the population - are in possession of a legal SIN, whether that's national, corporate, or criminal doesn't matter.
I believe that 99% of those who are SINless are scrabbling for enough food to keep healthy, enough shelter to keep dry, enough clothing to keep warm; the other 2000 people are shadow-denizens of various sorts, from successful ones to those just starting out.
I further believe that of those 198,000 non-already-shadowrunning people, few of them are going to be able to acquire literally tens of thousands, even hundreds of thousands, of nuyen in order to gain the type of implants or tech necessary to become a standard starting shadowrun character.
I believe that the people who are more likely to have acquired that sort of gear - or education, if you're talking high skills - are people who are in the system, who can join the armed forces, or be part of a corporation, or go to college. The magic types have it 'easier' in this regard; magic has no respect for persons, as the saying goes, and a kickass adept can get her training on the street as easy (or easier!!) than in a corporate facility. When it comes to those archetypes who require money, though, it isn't likely to come from the hands of the poor and downtrodden.
So I believe that, from logical progression and like most of the characters in Street Legends, Street Legends Supplemental, and 10 Jackpointers, the majority of people who become shadowrunners have had a valid SIN, whatever its source, before entering the shadows and burning it.
ZeConster disagrees, which is fine. He believes that most shadowrunners never had a SIN in the first place. I think that's utterly wrong, and from analysis of the following, my supposition of how that happens - street kid/ganger, 2nd Gen shadowrunner, or tribal - pretty much seems to be borne out.
The idea that most shadowrunners never had a SIN, and didn't have to burn one as they entered the shadows seems to me to be to be completely ludicrous. Any background that involves being employed by a corp is going to give you a SIN; any background that involves entering the armed forces is going to give you a SIN. But if in ZeConster's world (or the world of whomever is reading this) you can work for a large corporation or military and get tens of thousands of nuyen worth of materiel implanted in you without them keeping tabs on you by way of a SIN ... more power to you. Just not in my game, and according to everything I'm able to read, not in the standard Shadowrun world.
Unknown/Null: Agent (Because, well, Agent. Is currently a SINner.), Serrin Shamandar/Ire (no data, but DID go SINner for a while.), Hannibelle (inherited her father's cyberdeck when he's killed in gang crossfire, but buried her past thoroughly - might be a corp kid, might be a 2nd Gen shadowrunner), Hans Brackhaus (Null, shared ID), Street Rage (no info, but probably SINless street/ganger kid), The Smiling Bandit (wiped his past, but most likely an Original SINner, seems college educated), Ecotope (well-scrubbed past, but possibly Austrian national), Lei Kung (well-scrubbed past, but standard citizen is strongly implied), Orbital DK (scrubbed past, but she's in orbit - so very probably a SINner in the past)
Original/Hired SINner: Agent (probably), Cayman (standard citizen), Elijah (corp kid), Haze (employed by Telestrian*), Mika (standard citizen), Rigger X (corp kid), Sticks (strongly implied - geeky kid pretending to be a shadowrunner), Thorn (standard citizen), Winterhawk (standard citizen), Jonathan Blake (corporate fixer), Kia (corp brat), Yankee (standard citizen), Martin de Vries (standard citizen), Nadja Daviar (might've been street kid, but she became a SINner when she started interpreting for the Big D), Rael Whiteoak (standard/corp citizen), Cerberus (Dragon, corporate citizen), Hestaby (Great Dragon, national citizen), Lofwyr (Great Dragon, corporate citizen), Lugh Surehand (Immortal Elf, national citizen), Villiers & Lanier (Dynamic Corporate Duo of citizens), Hard Exit (corporate kid), Kane (standard citizen), Mihoshi Oni (V, soldier), Buttercup (free spirit, corporate citizen), Damien Knight (standard citizen, now corporate), Anne Ravenheart (possibly standard citizen, but definitely corporate), Baka Dabora (corp kid), Kay St. Irregular (standard citizen), Turbo Bunny (standard citizen)
Criminal SINner: Ma'fan (caught as a kid), Haze (caught as a kid*), Ecotope (got caught)
SINless: Akuchi (lawless area), Haze (Ganger kid), Kellan Colt (2nd Gen Runner), Marcos (ganger), Puck (otaku, which means street orphan at best), Tommy Talon (street kid), Bull MacCallister (street kid), Tess Van Hama (2nd Gen Runner), Mihoshi Oni (I-IV, VI, street kids), Slamm-O! (2nd Gen Runner), Harlequin (Immortal Elf, doesn't give two shits), Lyran (street kid and ganger), Man-Of-Many-Names (tribal), Riser (street kid)