There's a prevalent belief that a game being solo-friendly means friendships can't rise up or are perhaps forced to suffer.
The reality is that a lot of MMO endgame tends to force uneasy alliances, where the only way to progress after a point is to put up with people you really don't want to be around or tolerate game play that really isn't all that enjoyable. For those who don't want their entertainment to be marred by such, MMOs can be an embittering experience as one struggles to find a group where the personality clashes are minimal while the frustrations of play can at least be minimized by good company. Not everyone succeeds in this regard, and it's more of a thing in XI because it's not with the time on LFG tools and cross-realm functionality. And as I recently brought up in the XIV section, the $18 world transfer fee doesn't do the player any favors.
Generally speaking, those who aspire for solo-friendly just want to be able to log in and actually get something done. It's not that they don't want to play with others, but there's usually something about the process that complicates it. Using XI as an example, if you were someone that didn't want to play RDM as a main healer back in the day, you were going to have a hard time. People would use that preference against you, and even if they never actually played with you, the "reputation" of closed servers could be forged solely on hearsay. And while you might've had people who legitimately deserved ire, like those who ran off with LS banks, ninjalotted, and the like, the actions of a few bad apples do not legitimize hamstringing the ability of other players to get things done, particularly in a manner they find enjoyable, even if not in the coveted "most efficient" way.
Ultimately, things like this are a lesson XI learned much too late, and is perhaps why the WoW model took greater root in popularity than this or the Everquest type. However, even those games are stuck in the raid-centric model and the fear-mongering that raids would die if people didn't have to conform still exists. That tends to bring me to my ultimate point that if something is fun, then people will participate. If forced party play isn't fun, then something is wrong somewhere. And yes, how games are designed do influence our behavior, which could turn an otherwise pleasant person into a total buttmonkey when things take a turn. Stuff like lockouts and (steep) penalties for failure feed into that. Sadly, you'll have those who believe such things should also be present to encourage better play, when the reality is it likely doesn't and even discourages participation. So, yeah, we've got ourselves to blame in some ways, but no amount of personal tolerance or respect for others will change how things are coded.
Frankly, the RP element of MMOs has been lost. And I'm not talking about where you fit on the trinity with a given job/class. Rather, playing differently needs to be more valued, even if it occasionally means having strengths and weaknesses. And shining in those moments of weakness is what's going to make an encounter more memorable, be it a static party, guild group, server-only PUG, or cross-server match-up. None of the MMO Catch 22 crap. No more presumption someone's read a guide or watched a video. No more "skill-based rotations" that can mean performances are orders of magnitudes different from those who "get it" and those who don't. Some will groan at all this, sure. Some will resist the notion, absolutely. Yet, I'd posit it's all of this conformity that makes people seem so... disposable. And not because someone could do something on their own.
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Violence good. Sexy bad. Yay America.