A fixation I've seen in various groups over the years, is where a person or group of people try to force a particular gathering to be something else. That "The Cause" is all important and that everyone else must talk about. Most of the time this "The Cause" has a good reasoning behind it that many can consider it a good cause. The problem is when "The Cause" is being pushed hard on others as the pusher tries to bend all of their life and those around them to "The Cause".
All groups/communities have a reason to be, and a filter that defines them. They range from those who gather at a particular drinking spot (or watering hole) as the filter to just be social and gab about what ever, through to a gathering (often on-line) about a very specific topic (such as; propagating roses, supporting a specific bit of software, or underwater basket weaving).
The more general community will often be more likely to at least discuss "The Cause" and may even take it up as one of the group's causes for a while even if it triggers some members to not attend for that time. For a community about a specific topic, imposing "The Cause" is just plain destructive to that community for a bunch of reasons. For starters it changes the defined filter for the group to the detriment of what is discussed. If the "Mountain N-Gage modellers" group suddenly has someone insisting that every second car be a specific colour and all the software they use show a brand symbol of that colour, then that is just going to clash and not work.
Communities serving a specific target exist for a reason, with the logic of you pick the ones that match your need, and leave them when they don't. The reason can be for plain recreation through to maintaining different systems or support groups. I've been in on-line communities where someone is trying to get help with a system to help with "The Cause" and only includes how "The Cause" is so great and wonderful and never gets to actually describing what is broken, then complains that nobody is telling them how to fix the system. Nobody can help you fix a broken system if we don't get any real details about the system, as "The Cause" it is for is not even relevant for the task. This is why so many focused communities resist or ban "the cause that must not be named" just to stay on track. If you don't want to be on that track, go elsewhere and the track will still be there when you are ready to be on it. If the community lets the track be derailed, it will often flounder around and may not even survive. "The Cause" will have it's own communities, so don't be so shy about them but go play there for a while.
Everyone (assuming human and other mammals) needs to breath, to do something other their one big focus, even if just to re-energize to get back to that one big focus. This is why soldiers get R&R to re-energize before getting back into the fighting for their cause, and to even remind them of their cause. If one were to turn all their communities to "The Cause", then they'd lose the 'rest and rebuild' that comes from those communities, and hence just plain burn out and stop being effective for "The Cause". If you think people don't need to breath, then I invite you to be only "The Cause" you are pushing by not breathing. Breathing is always other than "The Cause" even if the cause is about enabling breathing. Getting in the way of others breathing, is a good way to make yourself hated and ruin any good thoughts those others may have had for your "The Cause" defeating your efforts.
All communities find their natural range. If it gets too big it gets difficult to have good conversations and they usually fragment in some way. Dividing into sub-groups for specific topics is a common way even if some of them are temporary, or another is a hard divide into 2 or more new communities. Sadly there is one other that may initially appear as one of those avenues or goes directly to just not existing as it fades away with most participants just leaving in frustration until all that is left are rants of "The Cause, The Cause" and then even those depart out of exhaustion and/or boredom. Having "The Cause" forced on a community can often be a trigger of such breakups and diminishing of the overall community if it doesn't block such forced attempts.
There is a term for those forcing "The Cause" down others' throats. While it started with a particular religious sub-group, Zealots is the perfect word for those whom are all zeal and imposing their excessive zealously on others. So if you find someone pushing their "The Cause" too hard, tell them they are turning into a Zealot. It didn't end all to well for the original Zealots, so it would be a good idea to tone things down some, to be more effective. There is such as thing as too much of a good thing. Water is a good thing we all need some of, but too much is called drowning. We all need oxygen, but too leads to deadly flames like in the Apollo 1 disaster
A fixation on "The Cause" is not unlike the draw of the One Ring in Lord of the Rings. Where all the goodness one attempts to achieve is undone and corrupted by others leaching off of those good intentions
One ring to rule them all,
one ring to find them,
One ring to bring them all
and in the darkness bind them.
Forcing a good cause can still lead one to darkness, most commonly just changing the flavor of the darkness you were trying to change in the first place. If you can't leave the breathing and healing places be, then you have become the darkness you were trying to defeat.