> So on one hand you believe that supporting one standard will necessarily come at the cost of supporting another (I don't),

So, you think vendors who have covered 99%+ of their userbase with a solution will generally also implement an alternative that is way more complicated for the remaining 1%?

> and you agree that what I suggested might cover 99%+ of the current user base, yet you favor a solution that depends on global addresses, something which definitely doesn't come close to 99% of potential users?

No, I favor a solution that does not depend on the global (non-)routability of an address, i.e., a solution that works for 100% of users.

> Well, if you want to be really anal about it you could call them "addresses which fall into one of the address ranges allocated for private use", but you're just splitting hairs.

But that is still equally misleading. There is nothing "private" about those addresses, and in particular nothing "more private" than globally routable addresses. Anyone can use those addresses, all the RFC essentially says is that you won't collide with addresses allocated by RIRs, but they might collide with other administrative domains that choose to use the same prefix. That doesn't mean that you cannot use them on a WAN, or between companies, or really anywhere where you can agree with all participating networks on the allocations. All it means is you have to expect collisions if you connect previously separate administrative domains, and that you cannot expect yout ISP to announce them for you on the public internet, that's it.

Also, just as you can use non-globally routable addresses between networks, you can use globally routable addresses for private networks, and you should if you can (which in practice means when you build an IPv6 network): Even if you build a network that is not intended to be connected to the internet at all, if you do have a globally routable IPv6 prefix allocated for your organization, you should number that network with addresses from that prefix.

> There is no guarantee, but that's different from saying that it's inherently unsafe.

No, it's actually not. "unsafe" does not mean "you will hurt yourself", it means "it has not been established that you won't hurt yourself".

> It's a reflection on how the internet is built. It doesn't matter that in the ideal network, everything might have an address, when pretty much every device is behind some kind of NAT. IPv6? Come back when it's widely adopted.

So, for the question of how to achieve (as close as possible to) an ideal network, it doesn't matter what the ideal network would look like?! Or do you think we should just wait until device vendors have screwed up IPv6 before we try to enforce some sensible policy?

> It stopped mattering because of address exhaustion and slow adoption of IPv6. Now, NAT is an integral part of the internet. I'm not trying to justify it or state this as a matter of preference—I'd definitely prefer having a ton of IPv6 addresses over the single IPv4 address I actually have—I'm just laying things out as they are, and how they are for the vast majority of consumers.

So ... because noone uses IPv6, you suggested to use ULA as an indicator for security?! I am not sure I follow ...

> No. Flagging a website as "safe" when it can not be established that it is safe is at least as wrong as flagging it as "unsafe" when it can not be established as being unsafe.

No, you don't establish "unsafety", that is the default assumption. The only way to establish that something is unsafe is to show after the fact that someone got hurt, which is just completely useless as a security mechanism.

> What I'm suggesting, not flagging it in any particular way at all, would be taking a neutral stance.

Wouldn't a neutral stance be to instead display a security status of "security unknown" (which is obviously equivalent to insecure)? "Not flagging it in any particular way" simply means that the user makes an assumption one way or another, not that the user thinks "it is unknown whether this is secure".

> IMO, the practice of calling HTTPS sites "secure" is itself potentially misleading to consumers. It is only secure in a very specific sense, likely not in the broader sense a layman would consider.

Well, yeah, but that is not really relevant to the question about warning about an insecure situation. Just because there are insecure situations that you cannot warn about, does not mean that therefore warning about other insecure situations isn't useful. Really, it makes much more sense to warn about insecure situations (which means, situations not known to be secure against certain types of attacks deemed relevant in the respective context) than to in display anything that says "this is secure", as security is alway relative to specific attacks, not a global property.

> The question I stop at is "why is my browser supposed to know that?"

Because your browser should help you protect your personal data that you process using your browser? I mean, I don't think it should know that, it should just enforce the same encryption requirements everywhere, but you seem to disagree with that because there are networks where your personal data is secure without encryption--in which case, your browser would either have to give up the goal of protecting your personal data, or it would have to know about which parts of your network are secure without encryption.

> Both a way of verifying and distributing certificates network-wide in a LAN and for those certificates to be usable globally.

Well, that would be a pairing mechanism then?! (Which still should not overload global routability with security semantics.)

> The premise of my suggestion is that the browsers won't back down from indiscriminately marking plain HTTP sites as insecure, hence "Perhaps a rather drastic change like this will lead to more user friendly ways to install self-signed certificates on home networks."—so suppose they would support such a method. Would that be better or worse than current practice?

It depends on the mechanism? Yes, centralized certificate management for your own devices would be useful, but it should not in any way overload the routability of addresses. If you want to use the LAN as a semi-trusted key exchange mechanism, that probably should happen at the ethernet layer. Or maybe with a one-hop TTL on the IP layer. You have to detect whether you are on the same LAN, not whether you are using an RFC1918/ULA prefix, because not all LANs use RFC1918/ULA, and nor all RFC1918/ULA are limited to a LAN, let alone a trusted LAN.

> That's a load of conjecture. I'm not sure how to respond except with a bunch of other conjecture, so I'll refrain.

It is mostly an observation of what always happens in such situations.