There's nothing stopping a group of motivated people from building a drone assembling factory that fits in a cargo container.
There may come a time where we have to stop outdoor festivals and parades because of people like that Las Vegas shooter from a couple years ago.
The real concern is when people can build a factory that can build the factory...
The only problem is that the novelty of the approach would be such, that it would bring too much visibility to the attack. Most bad actors don't want to be detected: "he fell from the window" or "his plane crashed" leaves the door open to coincidental causes. Drones are noticeable, particularly in swarms. They would be useful only in "showy" attacks, i.e. open terrorism, a tactic that is largely out of favor after 20+ years of substantial failure.
I’m somewhat gloomy about all of this. It’s just that war is war, it means killing people. Once it’s on, it’s on. So you need to be able to kill the enemy as efficiently as possible while minimizing non-combatant casualties before and after the conflict.
Long range artillery is the killer in Ukraine in terms of numbers, combatants consistently say so on both sides. But it doesn't have that wow effect of drone drop videos.
It has been the same say in WWI, anybody who read for example All Quiet on the Western Front would see it there. Not typical US wars against some poor fuckers with rusty AKs, but this one is very different and much more symmetrical. Something tells me that any symmetrical non-nuclear conflict these days wouldn't look that different to Ukraine.
The prospect of low cost swarms of AI enabled drones terrifies me. If you've watched any drone combat footage from Ukraine you know it's just around the corner, and this is another step in that direction.