Your attitude is that users who aren't tech-savvy enough to prevent things like this from happening deserve to suffer

Actually, from the TWC side of things, they do deserve it. As a company, we offer all the tools included with the subscription to keep your computer safe (ie. free antivirus, firewall, spam, etc etc), and we make sure to advertise this fact in all our promotions. However, people either choose not to use it, or choose to use it but then end up not configuring it correctly or otherwise disable it so the protection no longer works. What, are you saying that us, the cable company, should come into your home and force people to install our choice of software or bugger off? Granted, they don't have to use ours, there are tons out there, but if you choose not to use, don't blame us when you lose.

ike it's going to help TW's bottom line if they lose a customer permanently because he's outraged that they charged him $300 without (from his perspective) warning, and possibly lose some other customers because this one guy convinces them TW sucks

Again, just like users that use up all their bandwidth, these are customer TWC is rather happy to lose. These are also the same people that call us for credit when their router gets knocked offline, who scream on technical phone calls when they can't figure out they have to put their TV on "Component 1" to see their HD signal, and the same people who continue to request that someone should come out to their house this very minute because they are no longer able to connect to their VPN and they can't telecomute that day and are losing thousands of dollars a day because they can't browse eBay. (All of those last things are against TOS, btw, and require a business line if they want that kind of support.) These kind of people eat up other resources from the cable company and usually end up costing the company more in additional support and help needed because they just don't get it, and they never will.

these people still have plenty to contribute online, and cutting them off just because you think they're "lusers" is foolish and short-sighted

Granted, as much as I may want to cut them off from their service, I don't, because right now they are paying customers, but we do cut people off on a regular basis when they get infected with spambots or viruses or whatnot. The problem is that the customers refuse to do anything themselves to fix it or, if they can't do it, to hire someone else to do it for them. I have seen countless accounts of people who call in because their internet has been shut off and they're receiving our virus warning page, only to look at the account screen and see multiple notes from times earlier the same year of them being in the same situation.

So no, I hold no sympathy for people who buy and attempt to use technology they are either incapable or unwilling to learn to use. You don't go out and buy a car if you don't know how to drive safely, you don't go out and buy an electric generator without learning how to use one safely, and you not buy and use the internet without learning and at least attempting to use it safely.