. it is advisable to have one.
I asked 'Toosmokey' why he want's a firewall, and he is running linux, not outlook or things like that.
In my opinion, firewalls are the hype of the day.
Most private users don't need any server, so running a firewall is the wrong decision.
The traffic isn't away of your computer - it's on the firewall.

If you don't listen to a port, how shall your system get affected?
I don't run cgiemail and perhaps Toosmokey doesn't too.

Sorry, but I cannot find an argument in your post.

I don't start inetd automatically.
When it is started, the services are only enabled in the local net.
No need for a firewall at all, nor for an additional computer consuming power to make some noise and write funny logfiles.

And I don't need a router (with an additional firewall) too.