In general, I do find that forums dedicated to a single Brand are less toxic because everyone shares something in common. Those much more general forums though are 'toxic' because there is that tribe mentality, you must belong to 'one' tribe and the one tribe is better than other tribes. If you belong to 'tribe' PRS, then the tribes of Gibson, Fender etc are against you and that's where toxicity comes into play.
Its the same with Gaming for example. If you are on a Playstation or Xbox site, there is less toxicity at least not aimed at you because you belong in that tribe. Its 'fun' to take digs at the other and everyone 'laughs' because they are all on your side. The majority of the discussion is focussed on just 1 brand so most of the discussion is 'one' brand but if you also own the other brand, being pro-brand 'B' can sometimes feel a bit like some are quite toxic if given half the chance. On general gaming sites though, the toxicity is MUCH worse because all the 'fanboys' gang up and trade verbal blows either making out that their brand is better or the other brand is worse etc
The Gear Page is a bit like 'IGN' for Musicians who want to kick other brands when they can and make out their preferred brand is better. If your favourite brand isn't the 'biggest' seller, then you feel outnumbered and tend to feel more toxicity than the 'big' sellers with many more numbers who will gang up in support if you try and defend your self, your brand. AV forums can get bad because of multi-brand (Samsung vs Sony vs LG) and even multi-technology (OLED or LCD or Projector) and which has the best HDR, best PQ, best motion etc etc.
Single brand forums, especially the better ones with the better mods, won't stand for too much 'brand bullying' and often, the mods themselves may have more than 1 brand as well as many of the users too. They are quick to stop things escalating and the majority are often much more tolerant of other brands - even if they are 1 brand users. You also have to look at the top, in this case Mr Paul Reed Smith himself who would have absolutely no hesitation in buying a 'guitar' (or Amp as PRS make those too) from a different brand if he felt the guitar 'spoke' to him and that attitude tends to be echoed down through the rest of the PRS people.
There are a number of things that contribute to a great Forum and the more of those 'things' there are, the less toxic a forum is. This forum has a LOT of things that make it great - from the philosophy of PRS himself, to the mods that run this forum, to the members that are welcoming and tolerant (if you only own 1 SE PRS and 20 other guitars, you are still welcomed and not 'ridiculed' or targetted for owning different brands, made to feel bad because you only have an SE etc) and most important, helpful if you ever need 'help' or advice on anything. Even if there is a 'disagreement', I never see things degenerate into 'name calling', aggressive behaviour etc, just people giving their opinion and reasoning - if that fails to resolve in a 'single' agreed point, it invariable ends with an agree to disagree and move on with no animosity - at least that's how it has appeared to me.
A forum is as good as the sum of its parts - from the top with the moderators all the way through to every member. It may help that this is a single brand Forum rather than a free for all with every brand, but that still requires its members to be 'tolerant' of those people that may have and use other brands too. Members don't have to be Welcoming or helpful but if they are, then that also contributes to a great Forum and why I think this Forum is one of, if not the best I frequent.