As time progressed, certain scum tactics were discerned and codified into the set of ideas we teach beginners today, but in codifying them we have become stuck in our sense that those are the primary scumtells of the game. In the meantime, because we have freely declared what we deem as scummy we have given the scum all of the tools they need to obfuscate and confuse us. By giving them a specific set of scumtells to work with, they have a set of tools to attack any player they see drift close to one of those scumtells, and because they know who the scum actually are they are able to attack without hesitation.
I can't say I fully agree. It's common knowledge (at least among the veterans and most of the moderately experienced players) that that scumtell list, while not useless, is not representative of the current meta (being years old) and lacks both current tells we tend to identify and the subjectivity necessary in interpreting actions, while including tells that are largely rejected today (OMGUS being the best example).
As an explanation of the BM scum bias, though, this works well.
[...]we have this misguided view that town don't need to be concerned about their image when they DO, because their lynch does not help the town in any way.
While I see the "real townies don't care about their image" thing pop up still outside of BMs, I think we've mostly moved on to the more nuanced "town cares, but generally not as much as scum unless inexperienced" view.
Another problem is that many of the scumtells on the list are often extrapolated and blown out of proportion. If someone doesn't really have much to say on the current proceedings, they are accused of active-lurking. If they vote someone voting them, no matter what the reason, it's an OMGUS. These scumtells are intended as guidelines, but they are presented and used as hard rules. In reality, what makes a scumtell is INCREDIBLY subjective depending on the player being analyzed. For example, I wouldn't vote Tiruin for inactivity, but if NQT started lurking in the background without a given reason it would ping my suspicions fairly quickly.
This has been the classic newbie flaw since at least when I first arrived years ago: the "Look, a scumtell!" style of scumhunting. There is a statement in the BM OP spoiler, early on, that the tells are "very, very subjective," but it is underemphasized. Add inexperience/lack of knowledge of what makes tells strong, and the result is not great. We do need some changes to how scumtells are presented to beginners.
OMGUS accusations I know I, and several other veterans, largely don't take seriously. I don't think there is a single kind of accusation that gets more quickly and consistently shot down than OMGUS accusations. I see them a bit too often outside BMs, but I think I've only seen a few stand up under the slightest bit of scrutiny.
That is one of the reasons I pull batshit-insane gambits every game: it shakes people out of their complacence with the old ways of doing things. And in general, people hate it when I do them.
I can't think of all that many cases where people tended to strongly dislike your gambits. Only cases I can think of: Paranormal 24's PM thing (based on an overvaluing of a mid-range investigative role and collapsed instantly), KYOSN and the lever pull (where you got misblamed for my last-minute voting mode change), and Supernatural 7's big thing where you ignored nuance in voting (which was disruptive and distracting, the two things that consistently provoke the most anger in Bay 12 Mafia). I may be/likely am unaware of something, though, but when the benefits of your gambits outweigh the costs, I think people are okay with them. There's a reason people loved your Choose-Your-Own-Masquerade play.
And overall, we're evolving. Not as quickly as you want, and quite likely not as quickly as we should be, but we are evolving. Though massive strategic changes haven't been happening, there are significant matters where the general collective view is changing. (One big change I would like to see: an increased emphasis on lynch arguments as being to convince people, with greater acceptance of acceptance of arguments. There's an aversion to bandwagoning, I think, that keeps people from publicly agreeing with the points of others.)
As a side note, I consider you to play in the general Bay 12 style, with gambits being your main quirk.