Social discord
Something I regard as unfortunate about online spaces (barring outliers like Discord . . . to some degree) is that what I'll call "social compartmentalization" is impossible. There are more obvious issues (old jokes in poor taste being dredged up, expectations of "professional" behavior extending past working hours in an even escalated form, personal conversations being misinterpreted, bad faith report bombing) arising from the same sources (everything is said on a freely accessible public "forum" and never deleted), but this is one that's become more relevant for me recently, has always been concerning to me, and does not seem to get much attention (perhaps because acknowledging it may seem like some kind of confession to something or just selfish).
The basic gist is this: if you have multiple friend groups in the lifeworld, a reasonable expectation is that there will be very little chance that what you say in one group, or even the knowledge that you're involved in that group, will become known to the other group(s). The dynamics and language of these friend groups may vary wildly and are going to be relatively impenetrable to outsiders. The way you speak and act in one setting is fundamentally different from the way you speak and act in another, and this behavior is both informed by and itself forms the image of yourself that you present to each group. This all may appear dishonest on paper, but it's a very normal and even healthy way to operate within a diverse society.
I think I got a bit low-concept there, so I'll try to keep the rest of this succinct. Starting from where I left off, if we take those truths to be self-evident or whatever, we get the sense that disrupting this capacity to have a fluid group identity would be socially damaging by either straining the integrity of these individual group identities we act out or forcing us to try to fit into multiple groups with a fully consistent persona. Of course, this is exactly what happens on social media platforms. As your friend scrolls on Twitter, they may see you replying to someone in a voice totally at odds with the one you typically use around them. This will start to change the image of you that they hold in their head, shifting with it the dynamic of your relationship in a way that could be uncomfortable for one or both of you. Or, [a day passed between the parts written before and after this point; please excuse any interruptions in the flow] you adopt a static voice for every interaction and encounter limitations in your ability to integrate deeply into any given group because you're trying to fit a circular peg into an oval hole.
Another aspect of healthy, discrete social groups is the ability to gradually incorporate new members and to release members that create friction. If a member has a friend they'd like to introduce to the group, they can (usually with permission) bring them along to a gathering, which allows the group and the individual to go through a trial run of sorts—essentially, does the vibe match? If this is successful, the new member may be invited to future gatherings, and if it fails, then the individual will simply not be invited or not ask to be invited in the first place. After this, they won't have any knowledge of the group's activities in their absence. An (sort of terrible, but useful with a large asterisk) allegory would be the trolley problem—essentially, the individual or group's rejection is a passive rather than an active event. This could be embarrassing for either party, but it's hard to construe as antagonistic. There's also relatively little pressure involved in the act of invitation as a result of this, encouraging such attempts. And though it carries much deeper emotional baggage, the same process is possible with longstanding members of the group who aren't particularly interested in participating anymore, or who create issues. They can often be passively ejected or choose to halt participation without requiring any kind of confrontation, though they'll likely catch on to what happened and contact individual members to seek closure. They do say it's better to ask forgiveness than permission, though.
The two sides of this—passively blocking participation and passively blocking observation—usually cannot both be fulfilled in any online space, but typically the nature of that failure also means that it's unusual to find cases where both cannot be in theory fulfilled (depending on your definition). On public social media, the group may choose to ignore (and/or mute) an individual who continually tries to participate in their social interactions, a passive block, but that does mean allowing the individual to observe all of those interactions until they catch on. This can be damaging to their relationship with any individual friends in the group. Of course, if this behavior becomes repetitive, it may result in active/"hard" blocks which also constitute hard obfuscation of group activities, fulfilling neither non-confrontational aspect.
In private spaces such as Discord or even group chats, the act of inviting a new individual requires some amount of confidence in their ability to integrate, because they must by the platform's design be included in group interactions from that point on unless they leave voluntarily, active/confrontational means are employed, or the construction of the group space is altered in order to accomodate them (in other words, unwanted presences could potentially be highly intrusive). Despite its active nature, a new individual who rejects the group is usually able to leave without much ado, as most spaces do not have a leaving message and the individual is easily looked over in the member list. However, kicking this person, the closest thing to a passive rejection available to the group, is for obvious reasons going to appear confrontational. Furthermore, any longstanding members do not have the same ability to discreetly excuse themselves that new members do, because someone will notice their absence and inquire about it (since it must be to some degree abrupt). This can lead to periods of years wherein someone is a part of the group in name only despite having no interest in participating because they do not want to spark a confrontation. When this disinterest is a result of confrontational feelings that they simply don't want to act on, that small resentment may fester and lead to an explosive departure which leaves some group members scratching their heads and is incredibly damaging both to relationships between the individual who left and group members, and to group cohesion. Another side of this is when the individual is a problem for other members of the group but has no interest in leaving, especially when that individual is very close with other members. Actively rejecting this person could cause collateral damage to the roster, but failing to do so can similarly create a process of decay as the group becomes "toxic" and therefore uninhabitable to the members for whom the individual is an issue.
These last two dynamics, in my experience, can be incredibly destructive for online social groups and are regularly the greatest sources of tension in the Discord servers I participate in. Besides the personal (self-serving) nature of it, this is why my own Discord server is under a tight lock and key, and any new members must be 1) known to me, 2) on friendly terms with anyone they know in the server (to my knowledge), & 3) of a disposition that I think would integrate well with the established community. There have been exceptions to this rule in the past, and I have always regretted them. There are several people whom I'd like to add personally, but whom I do not feel would be a welcome presence (or feel welcome, alternatively). This is why I do not advertise the server very much, and why I ask those who know about it not to take me declining to add their friends personally. The more time I spend in such spaces, the stronger my conviction about this point becomes as it is frequently proven right. ~∓~