On people giving without taking : Someone taking without giving would be someone sitting around without doing anything. It does not exist, people do things, and most of them are useful to the community. But let's admit some people just sleep and eat, or let's admit that you consider people that give less than they take a problem (which it isn't in anarchy, it is not a meritocratic system) : if that's just a few (closest to reality), probably not a problem. If it is more than the community can support, then it's a problem the community has to solve with anarchic means : try talking to get some of them to do stuff, try getting help from other communities,etc. If in a very weird world, it does not change anything, then you just have the possibility to provide help and resources for participative people first.

Anarchism relies on self-interest magically aligning with collective good. No, that's precisely the point i'm trying to make. You are not helping selflessly : you are helping each others, so that they are able to help you. You can be selfish in an anarchist community : just do the bare minimum, and not help for collective actions. It does not break the system. Even if everyone does it, as long as everyone do the minimum, everyone get the minimum. This is something that works out of the box for everyone : whenever you do stuff with friends, family, neighbours, be it playing football, repairing something, preparing a party, in an informal manner, then people organize by themselves. Some do more, some do less, almost everyone does something. Unless there is a strict hierarchy in the group, when the popular friend or patriarch might then do nothing.

On preventing power : Your point is that armed struggle is necessary to prevent power, and you then equate prevent power to make the system work. Again, preventing power is not about how the system works, it's about how the system survives. The difference between current systems and anarchy is that coercion is not needed to make the system work day to day, it is needed in its most primitive force when the system is threatened. Also, you directly skipped all the solutions to try beforehand (educating the people to what power is and how and why to prevent it, watching out symptoms of power, etc.) to just sum it up to "violence", which is the last resort option. Another difference from the current systems.

On capitalism : it's all good, i get your point of "it's the more likely regime to survive, so be it", and i'm fine with it, it's a valid point of view, especially nowadays. I'm just struggling with why you need to establish that anarchy has to fail on its own (rather than against power/capitalism) to prove it.

On "pure" anarchism : You could be right to call out "purity" behaviours, they are common in far left movments, i acknowledge that, especially for myself. But here that's not the case : they are clearly not functioning with anarchist principles, like i explained it's simply impossible to do because of the concept of server. They are anarchists using non-anarchists means, just like some royalist parties take part in republican systems.

As you are very cautious about what your intentions are, i should be too, my bad if it comes late in the discussion : i'm not saying anarchy is the best system for every one, i'm not saying it's viable as it is, i'm not saying it is a perfect thing that hurts no one. I think it is the best for me, would be the best for most people weren't they born under capitalism, and that's it's one of the less dangerous form of politics. I understand it has to face powers far more violent and dangerous and therefore far more likely to survive, and i also understand that it has to be conceived from within societies full of capitalist and pro-state assumptions. My main goal is to get you and people to a nuanced take on anarchy, notably that it does not fail inevitably on its own, but is very likely to fail because of capitalism, and is likely to fail on its own if you want (but not inevitably, that's the absolute i'm trying to fight here).