I mean, Once is definitely not the only fandom that has this problem, but the show's supposed to be centered on family and fairytales. Instead, it now seems that the fandom and to an extent the show only cares about the ships.

Namely SQ vs CS vs OQ (and some times Swan Fire).

Honestly here was a time when I was a part of three of the above fandoms but now I don't really want to be associated with any of them. I mean we have CS fans tweeting Lana calling her 'Lana Parrillaids', we have SQ fans constantly harassing the writers and shit talking them, we have CS fans saying that they want Lana dead, we have SQ fans who got Happy's actor fired from Once and to quit acting all together, we have OQ harassing SQ fans. All three fandoms are being awful and immature in different was.

And when the harassment isn't going on they knock and nitpick favorites and tag it all the time. For instance everything Regina does is 'rapey' or 'abusive'. When she killed the count it was evil--ignoring the fact that she saved the Charmings. Hook is also 'rapey' or 'abusive' or 'sexist'. And Emma 'isn't really Emma anymore' or has 'become a weak damsel'.
And the whole 'h00k', 'C$' thing gets old. I don't even ship that one. Likewise with '$Q' and 'r0bin'.
Naturally this leads to more fighting among the fans.

I've gotten to the point where I found myself thinking; "if you're only watching for OQ he's dead so you may as well stop if you're only gonna complain." and "if you're only watching so you can complain that SQ hasn't happened yet, then why watch at all." Neither of these groups seem to actually like the show. They literally watch for the ships and not the plot or the characters as individuals. When did this fandom start watching for ships and ships alone?

And it has started to impact the show too! Due in part to SQ fans pestering A&E, particularly in regards to 'unintentional' and pointing out ever scene where the two are ever close and calling it 'eye sex', we can't even have Regina and Emma standing near each other on screen because A&E (also being immature at this point) have apparently decided to create no homo space. It's like they're trying to retaliate to.

That ship war aside, even Rumbelle plays a roll due in part to how bad the authors screwed it up. A&E want so much soap opera-esque ship drama that they took a perfectly good ship and broke it apart. Literally Snowing is the only ship that's sailing good. I hope that sticks.

This show has become so focused on ships everything else is lack luster. I mean Zelena was tossed with Hades for the sake of her having someone? While she hit on Gold. Henry was tossed with Violet. Ruby with Dorothy. The Evil Queen with Gold. Even Hyde's story was centered completely around romance.Like they are putting way to much into shipping and not enough into developing the story or the characters individually.

*Goes back to shipping Stable Queen where it is safe*

But like you said anaswill, this isn't the only fandom like this I've seen it with HP and Avatar. But none of them have harassed the creators and actors like the Once fandom.

I wasn't a part of the fandom when the show was on TV and the fandom was most active, so I don't fully know how bad it became, but I have seen some examples of fans taking shipping too seriously. I don't know how strong it was though, or how pervasive it was throughout the fandom - maybe I'm being optimistic in hoping it was just extreme fringes?