I have one major issue with the article. It needs some qualifiers.
Because it is pretty reasonable if the target audience is home computer users. Your home computer isn’t really getting much out of a firewall. The biggest threat to the home user is malware, and most firewalls aren’t doing much to protect you from that. Now, if you have a firewall with application whitelisting, that will actually be quite useful, since it should stop any malware from communicating back to a C&C (command and control) server. This is usually too much of a pain for your average home user to administer, though.
However, if you are talking about government or corporate networks, you definitely need a firewall. Firstly, you are a potential target of foreign and domestic corporate espionage. It wasn’t too long ago that there were reports about how the Chinese are infiltrating our corporate networks and making off with data that eliminates any competitive edge. If you don’t do business with China or Eastern Europe, why not block all of their IP addresses at your firewall? Sure, they could use a proxy or Tor, but it will weed out a number of automated attacks.
Your corporate network can have hundreds or thousands of servers on the Internet. A firewall filters traffic out that doesn’t need to go directly to those servers, protecting their bandwidth and processing power.
Finally, a firewall not only blocks attacks from the outside, but it can also block actions from within your network. This will keep rogue users from setting up unsafe services that could be easily compromised. Also, as I mentioned for home users, application whitelists can prevent malware from communicating out. This is even more important for a corporate or government network. One compromised machine can be used as a pivot point to access the rest of your network if it can be remotely accessed. If a machine gets infected with malware, a firewall could prevent that malware from communicating out (plus, alert the network administrators that the machine has malware installed).
So, to conclude, your average home user doesn’t really need a firewall but that doesn’t mean that firewalls are not an important piece of network security.