Should people be able to (down/)vote in communities they dont subscribe?

Yes.

If your admins consider down-voting an act of hostility, maybe they should disable down-voting on the instance. Did they consider the possibility that those accounts they banned were bilingual, and simply prefer to interact in English?

Without the context of the post, the actors, etc. it's hard to justify a position other than, "this is working as intended." Randos bulk downvoted a post, the spike in downvotes prompted mod action. Everyone got to participate and suffer the consequences of their participation.

Another interesting concept that came from the discussion over that was “constructive downvote” - requirement of commenting why one downvotes a post.

Speaking only to this…

Hexbear chose to remove downvotes, and the “dunking” comments came to replace them. Getting ratioed is a thing, which purportedly started on Twitter.

The consensus on Lemmygrad came to be that (and I’m paraphrasing because I’m not sure of the original phrasing) “dissent without elaboration” is valid. We don’t always have the time or energy to articulate our dissent (and sometimes gish gallop doesn’t deserve it).

I see two "deep" issues here.

One of them is that it's damn hard to decide, in online communities, who should [not] be allowed to perform some action in a fair, transparent, and simple way. There's always some way to circumvent it, and always someone who should perform it but gets locked out.

For example: what would prevent me from subscribing to a comm, downvoting everything there, and then unsubscribing from it? Or just subscribing to comms to vote-brigade them, while newbies legitimately interested on the comm are unable to vote in it?

I have no good solution for this issue.

The second one is that this sort of Reddit-like voting system doesn't really work well. It's at most bidimensional (score vs. controversy, or up vs. downvotes); and yet there are a thousand reasons why people vote, and a thousand pieces of info that they can retrieve (or falsely believe to retrieve) from them. And depending on those reasons, the vote might be completely fine or not.

There are also more practical concerns; I believe that @davel@lemmy.ml's Hexbear example illustrates this well. If you anyhow hamper the ability to voice negative feedback through downvotes, people do it by noisier ways.

For this issue, perhaps a "reverse Slashdot" system would work better? Basically splitting the downvote (but not the upvote) into multiple categories (e.g. "disagree", "this doesn't contribute", "this is factually wrong" etc.). It wouldn't prevent this sort of voting brigade, but it would discourage it a tiiiny bit (you'd need more clicks per downvote), and make it more obvious.

Yes, it's fine.

If you have vote brigading, ban them, take it up with the instance admin, and defederate, in that order.

If the community is public and shows up on All, then yes. I don't know if lemmy has private sublemmies but if they do, that might be the solution you are looking for.

Would it really matter? It's just as easy to subscribe and then say/do whatever. Only accounts that have been subscribed for a period of time? Subscribe and wait. Have a certain post and/or comment reputation? It's not terribly hard to speak to a specific audience and accomplish that. Make any of those extra parameters too severe, and you limit the community growth.

Crowdsourcing of ideas means that bad ideas are no worse than good ones, and in an evolutionary way, they're probably better at replication, strength, retention - and when a core tenet of that "bad" idea is that you must actively reject the opposing good ideas, that's how bad ideas overtake good ones.

If it was deliberate as you say it wouldn't change much, they could just hit subscribe, downvote, then unsub.

Another interesting concept that came from the discussion over that was “constructive downvote” - requirement of commenting why one downvotes a post.

I think I like that idea.

One thing that would be useful is having the per comm option to disable downvotes. So comms vulnerable/liable to this can just turn off downvotes entirely

I downvote non-English results I see on my All page as a punishment for not correctly setting the language on the post, which takes 1 second to do and would ensure it doesn't spam the feed for non-speakers. I can't imagine I'm alone - was the post in question not correctly tagged as Polish content, like your post is correctly tagged as English content?

If it was correctly tagged, then those downvotes were all from people who speak Polish.