Firewall: Yes? No?

Jim Hamm started the discussion about Firewalls with, "You may have already read this article. In recent years not much has been written about firewalls — one way or the other. I leave mine turned on in my Macs and when running Windows on my PC. Ubuntu doesn't come with a firewall and I haven't checked to see if one is even available."John Carter sends this information, "The purpose of a firewall is to keep someone from hacking directly into your computer."  He goes on to explain in detail. "Without a firewall, a computer is open to attack even if you have an Anti-Virus application installed on the computer. In fact, you don't even have to be browsing the Internet to be hacked if you don't have a firewall; the computer just needs to be turned on and connected to the Internet. "However, a firewall is not a guarantee to stop spam and viruses that come through email or when browsing the Internet. An Anti-Virus application is best for that. Ubuntu does have a firewall, but it is not enabled by default. The firewall is ufw. "If you have a server (one computer providing access to the Internet for other servers in a network), the server is the only computer in the network that needs a firewall, unless a given computer in the network wants to block a port on that computer for some reason. "All new routers (and some modems) come with a firewall (a hardware firewall) and it is typically turned on by default, and this is probably the only firewall anyone ever needs. In fact, a router with a firewall is recommended, even if you only have one computer and if the modem itself does not have a firewall. "However, the modem/router may not have the features and/or flexibility that a computer firewall (a software firewall) can offer. "If you have both the modem/router firewall and the computer firewall enabled, and if you have ports open for access in the computer firewall (required by some applications), those same ports need to be open for access in the modem/router firewall. "It's a little more complicated than this, but the bottom line is that the author of that article is off-base about not needing a firewall. However, he is right about one thing: 'Firewalls tend to be horribly managed.'" John winds up his view of the issue with,  "If something isn't working right and you turn off the firewall and things start working right, call an IT professional to properly set up the firewall. One such professional works at CompuTime in Prescott." Anyone else jumping into the discussion?