Chapotraphouse

If you mean the people that dream of a world without writing or smelting or farming, then these are a very small minority, and their positions lean heavily on their ethics and not so heavily on viability. It's the same thing with the nihilists: in the absence of any plausible path to triumph, they quickly reorient around being as anarchic as possible just in their own lives, and don't have any horizon beyond that.

To be fair, it wouldn't be a stretch to say that a lot of our modern technology supply chains are headed towards consuming themselves out of existence. Within the coming century the ROI on mining oil, copper, lanthanides, and even construction-grade sand is going to drop precipitously below the point where we could feasibly integrate them into everything. It wouldn't firmly make our electric technologies impossible, but it would rarify them and prevent them from being maintained in a global economy. If humanity doesn't play its cards right, we'll end up largely stuck in the equivalent of pre-Industrial Revolution for a very long time.

But if you mean people who emphasize appropriate technologies with minimal supply chains that drasticly limit alienation and allow for pan-human projects to be transmitted and perpetuated... hi, I'm an alt-civ autonomous communist (close overlap with anarchism but I don't reject all hierarchy or power structures), and I consider it as close as you can get to primitivism while still being honest and serious about the progression of humanity. My stance is "it is possible to eradicate poverty and have a decent life with just glass-pane level of technology, but it would be nice to preserve computing if we can". I lived on an off-grid commune for 2 months, where we achieved a kind of communal luxury with 1/5 of the water and less than 1/10 of the electricity that a typical Western lifestyle entails; about 30 people got all their electricity from a couple square meters of solar panels and our day-to-day material needs could feasibly be met and supported within hiking distance; my retirement plan is something similar. I suppose my outlook would be a lot more interesting to you than purist "an-prim".

Potable water is a softball, all you need is pottery, and you can make a slow sand filter that catches anything down to 1 micrometer, maybe even a bit smaller. With a pulverized charcoal layer, a minimally-maintained algae layer on top, a sedimentation basin, and at least one drip transfer, you can catch most pollutants, most pathogens, and even most heavy metals. But as long as you don't shit near where you eat, a lot of the big threats simply aren't present.

Antibiotics is in some ways less daunting than it sounds. The biggest reason why we need them in the first place is due to widespread dense animal agriculture* and cities that don't allow for good sanitation. Many of our permanently useful medications came from indigenous plant knowledge, e.g. quinine. Since penicillin has been invented, it's a lot easier to envision maintaining it as long as we keep the knowledge, versus discovering/rediscovering it in the first place.

This orientation consists not of being afraid of the boogeyman in the dark of being invaded and overrun, but understanding the source of any potential state threats and maintaining a way to make it practically or strategically or economically unsuitable for them to extend their control over whichever territory in question.

*A lot of things boil back down to this recurring situation where the trajectory of our civilization has created difficult problems that we instinctively turn to the same civilization to solve. At any rate, the question of how to abolish carnism is a far more challenging one than the question of how to prevent/interrupt the supply chains that tyrannical states need to operate.