I pointed out that it's easy to design cryptosystems to be unbreakably strong against all adversaries except governments, and indeed can be unbreakably strong against mass eavesdropping by governments, yet still provide access on a case by case basis. And in fact this is the outcome of all kinds of natural and widely adopted designs.
You're arguing that governments won't content themselves with such access. That's a different question entirely. I think many of them would and that we're heading in that direction, more or less, where mass decryption of TLS isn't done by most governments and the era of GCHQ/NSA style bulk wire tapping slowly fades away, but it doesn't matter to them much because they can still warrant the other end and ultimately that's what politicians feel safe campaigning on.
Considering that governments are made up of people this would be quite a trick.
Regardless, even if it were so-- the objective would be to be unbreakable strong except to lawful and transparent actions of governments. The lawfulness of an action is undecidable by a cryptosystem. And we know that government frequently behave unlawfully.
Moreover, since cryptographic communications can be hidden very completely unless free access to computers and communication is almost completely suppressed; those who really want (and can afford) communications which are secure against government intrusion (lawful or otherwise) are able to obtain it. So the decision to purposefully weaken cryptosystems has the primary effect of amplifying unlawful intrusions by governments (and paries that steal the governments keys).
Is it? How? Because that's certainly not the default that you referred to.
Imagine you own a webmail company. You secure your SMTP relays with SMTP-TLS (let's pretend it works well) and your client connections with TLS again.
Now your users are safe from random creepy flatmates, criminals with wifi sniffers, your telco and even mass government surveillance. But, governments can still serve a warrant on you to get email in a targeted manner, assuming they have a working MLAT process.
All you did was apply ordinary encryption to an ordinary website and you have that middle ground between "unbreakable to everyone" and "totally useless".
It's easy to confuse that with the name of a programme to reverse engineer and analyse Google internal traffic (which is presumably now over as all that traffic is encrypted), and I made that mistake myself, but I was corrected on HN no less by someone who is closer to the leaks than I am.
It wasn't something done with the knowledge of Google or Yahoo, as evidenced by the use of reverse engineering of the data formats.
But that's the point: we've seen that this balance doesn't exist, because if the service providers have access to the plaintext, the State will not contain itself to issuing case-by-case warrants - see Room 641A, "SSL added and removed here", etc.
The current move to encrypt everything is a reaction to the realization that the balance that was thought to exist, does not, and political participation is not sufficient because the information is kept hidden, so no informed political discourse is possible.
But that's the point: we've seen that this balance doesn't exist, because if the service providers have access to the plaintext, the State will not contain itself to issuing case-by-case warrants - see Room 641A, "SSL added and removed here", etc.
The current move to encrypt everything is a reaction to the realization that the balance that was thought to exist, does not, and political participation is not sufficient because the information is kept hidden, so no informed political discourse is possible.