It's not that I'm casting doubt on Mr. Cerf's assessment, but I have no doubt there's a lot of simplification taking place when discussing the lack of security built into the Internet and its infrastructure. Secure communications inside the US have always been the redheaded stepchild of information security, before 'information security' was a thing.
In the early 80's I did my post grad internship at a company that made and serviced harbor control equipment. I spent seven months at Naval Station Norfolk as a result and it was so common for 'secure' Naval transmissions to bleed over into commercial transmissions there was a little dance everybody did so we could say that environmental condition kept is from paying any attention to what was said. By 'everybody', I mean everybody. The Navy liaisons, the harbor master and his staff, even the unionized teamsters and longshoremen, it was ridiculous to the point of hilarity, and it was deadly serious ship to the Navy guys. I don't know why they even bothered to come ask what we had heard and what we understood, but they did. Nobody was going to say 'Hey, yeah, I heard the announcement that President Reagan was actually already aboard, and the flotilla was just for show'. That's what we heard, but you don't go volunteering that. It was all the time too, not a rare thing. When the long deployment submarines were coming back in it got even more serious, 'Commies' were everywhere then you know, but that didn't stop anyone from broadcasting the entire production to every radio within a 100 miles or so. Although it had been 'proven' that your children's elementary school teacher or your family doctor could be a Commie, the godless bastards apparently didn't get into the maritime or logistics careers.
Same with federal law enforcement communications. The Navy (hilariously) brought off shore radio jamming equipment to Waco, Texas after it became evident the wackos were listening to radio communications. The Navy did that because those guys still practice semaphore, no shit. I still wonder how many times 'set the fuckers on fire' was danced out before confirmation was reached. Eric Rudolph is a major figure of study for military 'insurgent warfare suppression' and asymmetric warfare students and all kinds of shit was talked about how he was a super soldier and was using the US military's tactics against itself. Nope. He had a radio. A $400 Honeywell radio from Montgomery Fucking Ward. When the radio failed he lost his information source so he got caught in the dumpster looking for dinner.
DEA, CIA, FBI, Postal Inspection Service, Freight Railroad Police all the way down to Mayberry RFD had their comms blasted out to anyone with $75 and a fetish for procedural etiquette, or a drug operation, could listen to. Look at the biggest expense category of the post 9/11 'homeland security' grants. It was radio systems for local police departments that didn't broadcast on 'secure channels' any CB radio or police scanner could pick up.
Are you a jihadi who wants to know what commercial aircraft are flying in your your area and the lady at the ticket counter isn't helping? Pop on in to the public terminal that every airfield in the US has sitting out for you to check traffic, weather and martyrdom opportunities when filing a flight plan. Need a boxcar full of highly enriched uranium sent fresh from Y-12? No need to bother CSX, just look up closing times for sidings along the rail line route.
My point is, that things that have been around a lot longer than the Internet and deal with real deal, no bullshit dangerous stuff are 'secure' in the sense that a locked cigar humidor or locked gun cabinet with a glass door is secure, or a Jeep with a soft top is secure.
To think that the Internet was 'almost' secure in its initial form is like saying Neil Armstrong almost established a colony on the Moon. The DMCA was signed into law with a smirk and the knowledge of Congress that this Internet thing was just a bunch of shit but hot damn! Those contributions from the entertainment industry sure do make buying cocaine and hookers a lot easier.
I'm sure there were discussions about 'perfect' scenarios and 'unlimited funding' talks over beers like occur within any group of like minded people working towards a common goal (here where I work, we talk about solutions to problems one would experience trying to turn absurdly long things on a metal lathe of colossal size). We could do it, or at least we believe we know the best way to go about doing it, but that doesn't mean we're almost about to do it except (reason). There are about 53 million reasons why we aren't about to do it, cost being a really big factor, just like costs of secure information have, historically, never really been very high on the pork payout checklist.
Until this century secure communications and information security inside the US was generally viewed about the same way big banks view financial regulations. Inconvenient, and if you can't abuse the system for your own gain, completely useless. Deliberately confusing jargon and the use of arcane contextual indication systems (security through obscurity) were greatly favored by our cultural heros. George Washington, Thomas Jefferson, Benjamin Franklin and Theodore Roosevelt all favored hiding valuable information in plain sight through the use of clever systems of occulting meaning behind a facade of seemingly unrelated information. They wrote about it, forced it into the daily operations of government and it has remained at the core of our international and military culture.
That's begun to change, somewhat, but only since 9/11. Computers have changed the level of cleverness available to the 'unlettered man' (or very lettered terrorist :). But four decades ago? No. The locked gun cabinet with the glass door was considered more than adequate. I'm glad for the change, but we're a long, long way from having information security be anything more than a checkbox on the same form that has things like 'citizens right to privacy', 'justice' and 'rule of law' on it. In the 1970's they didn't even have the forms yet.