That seems like a broad generalization of both past and present day fans. Fandom has probably always included all sorts of people, not just the skinny bookish socially awkward stereotype.
Precisely so. The idea that fandom, of anything but for this purpose Star Trek, was a unified whole is, as stated, a generalization that I think may only have been true when TOS was the
only Trek. I didn't grow up when TOS first ran, but I discovered it when I was younger. My dad enjoyed it and had the Concordance and episodes recorded on VHS. I was glad to discover friends in middle school who liked Star Trek, but even they made fun of me from time to time, for various differences that we had over TOS vs. TNG (no other options).
To this day, my dad has not seen TNG nor has a desire to watch it, and I have other friends that are his age that feel similarly, though they like Abrams films well enough (the phrase, "Not your father's Star Trek" felt odd to me because of this).
I don't think its a matter of fans entering who might have mocked Star Trek when they were younger. I think the fact is that there is a variety of Star Trek out there now, and that there are preferences. People don't like war episodes? "Errand of Mercy" where Kirk identifies as a "soldier" is one of my favorites, followed closely by "Day of the Dove" and "Balance of Terror," the later of which is submarine warfare without the water.
The idea that DS9 is solely responsible for "darker Trek" is also hard for me to reconcile. Look at TWOK and the near horror style moments on Regula 1, or Terrell's murder of a scientist on screen. How about TUC where Starfleet Admirals conspire to assassinate heads of state? Even TNG was not spared darker facets, between the Borg and Cardassian hostilities.
As much as I would prefer a unified fandom, in this day and age, where there is so much variety, it simply is not possible. There will be divisions, disagreements, agree to disagree moments, and the like. Abrams Trek wasn't the first and it won't be the last.