Lemmy is "uncensorable" and offers identical moderation abilities in the "public square" aspect. E-mail is "uncensorable". Uncensorable does not equal unmoderated. It means if you want to publish something, nobody, not the even the government, can stop you (though they can throw you in prison but that's outside the discussion of protocol). It doesn't mean anybody has to choose to listen to what you publish. It does not mean relays have to include you in their list of public tweets. Relays can pick what tweets/etc they show. They can choose what goes through their relay. What they can't do is stop you and another user from using the protocol to DM each other. As long as one relay allows your traffic through, the traffic will flow. They also can't stop you from tweeting, they can just choose not to show your tweets. If I want to follow somebody, frankly, it should be no business of a relay operator or the government or anybody to prevent me from following them, just like it should not be the business of the government to decide what books I am legally allowed to read. By building networks which are "uncensorable" we can guarantee that it remains not their business for future generations. So that they can live as free, or freer, than we do.

The internet, as a structure, is "uncensorable". This is good. Power should be decentralized. The whim of a government shouldn't dictate how the entirety of the internet operates, and it can't. People in power love censorship, it is to their advantage that we are not able to organize among each other using common communication platforms.

While I can see the value in speech that doesn’t exist at the whim of our corporate overlords, these are people who’d get beaten up if they tried to speak the way they do online in front of real people.

Still some of those, as with any social media platform. I have come across a few objectionable things, I just blocked and moved on. But you pick who you follow so you pick who shows up in your feeds. Each relay has their own moderation policies, so (like Lemmy), you can pick relays which suit your moderation preferences (which effect the "trending notes"/public square section). Most nostr apps by default upon install will ask you if you want to automatically filter out crypto/nsfw/foul language/etc. I picked at random and didn't enable many of the filters.

It definitely started as mostly crypto bros, kinda like how lemmy was 100% tankies, but it's gotten better. Lots more human rights activists and scientists and even just regular people on there now. A lot of human rights/privacy activists/orgs are joining up to it after nostr got some promotion at their conferences. Ultimately your feed will be who you follow so luckily you're in control of that. The default settings for most nostr apps even include a filter to remove anything crypto, NSFW, and other controversial topics related.

Still very early days for all these platforms.

DMs aren't as relevant in Lemmy so I get why securing them isn't a priority, but in Mastodon or any twitter clone it seems like a relevant feature I'd like to have some security/privacy with. Instance admins, and anybody who breaks into their server, being able to see all DMs seems like a security flaw that should be engineered away. Even Facebook, the place with the worst privacy, has E2E encryption (or so they claim, who really knows)

Finding good people to follow has been a challenge for me both on mastodon and nostr. But I find just posting and seeing who likes my posts and then following them has got me a decent feed curated at this point. And searching hashtags for topics I'm interested in.

There are some bridges so you can follow mastodon users on nostr and vice versa, but it's not quite the same. We're still pretty early adopters on both platforms at this point.

Nostr isn't a Lemmy alternative, it's a Mastodon/Twitter/BlueSky substitute with more decentralized, secure and private features and i think OP should have pointed that out.

And since Op was comparing the secure and private features of both protocols, ActivityPub surely has improvements to implement for greater privacy and security.

Almost ready for it’s prime time I think. We just need a bit more on the UI/mobile app friendliness to make it shine for all.

Yep, been using it for a few months now and it's getting really good. Not quite as polished as mastodon (as least in the app I'm using), but still very fully featured.

Why do we even need relays in the first place?

To store message content. To hold message content if you send a message to an offline contact and vice versa. To handle getting things across networks (clearnet to Tor and back if you only are connected to one). To work around NAT etc. To moderate "public square" type features (ie trending posts). Many reasons.

What if one relay is on clearnet and the other one is on Tor?

No problem, relays can communicate cross-network. They relay things between each other so traffic will find a way through as long as one node speaks to both networks.

What if relays I use are not rechable by my contact, that lives in censored country like China and can only connect to relays in there?

As long as there is a relay path between you and your contact, there is no issue. Relays can be run through Tor and other anonymity networks which are very difficult to distinguish from other forms of encrypted traffic.

Why do we even need relays in the first place?

Same reason you need an email server, not everyone is online at the same time.

Closest I've seen to something truly serverless is plebbit, which is a Reddit/4chan clone using ipfs.