Ummm.. lol. No, the internet isn't necessarily "mission critical" when it comes to the personal user. That's still a matter of opinion. if it were as you say, it would have become a regulated utility and at this time, its not.
But, it's funny that you bring up how the internet has changed. What exactly changed the internet to make it, as you claim, "mission critical"....? Is it the fact that BUSINESSES have moved towards an internet model and charge people extra for services when they don't utilize it such as airlines and reservation fees? (There still isn't really anything you can't do over the phone that you can over the internet, and I'm sorry, a telephone "fee" doesn't validate the internet as "mission critical" between the end user and a business) But, the fact that people have turned to it for business.. that would mean that once again, "BUSINESS" has shaped policy in this country, and I thought that the majority of users on this site didn't like that - so fight it!! Fight the change that business is forcing on us... (I smell a double standard)
Outside of what I just said, business to business is still important as is government and those sectors are still operating just fine outside of all this outcry by end users.
But, the internet is still , be definition, a bunch of private networks connected together. Have you not noticed that there really is no one central point of failure in the internet? If a network drops off, you don't kill the whole thing. And, for the "internet" to work, you could technically pull the root servers for DNS down as well.. the "internet" would still function. The "internet" isn't domain names, it isn't FTP, it isn't email.. it's everything together "connected".. so you're right, the national highway system is an inter-connection of a bunch of private (and public) properties.. so thank you for acknowledging my point.
But as for how it affects people.. you're right - it does... but life, for the end user, would go on with out the internet so long as the telephone continues to function.
What I'm focusing on is the fact that those companies that "control large pieces of *the infrustructure*.." actually own it.. it's theirs to control...
I think your main focus is actually on internet access providers.. and not necessarily "the internet".. again, the internet is everything that is connected - period. That will never change.