[drdaeman]

One (usually) don't roll their own firewall. One's provided with a robust solution and merely needs to configure it - that is, provide a description of their network. Because no matter how smart and well practiced software authors and distro builders are, they still don't know about your network and your needs. They only could provide tooling and examples to make some common concepts easily achievable.

And configuring your own firewall isn't rocket science that should be left to pros. Especially - as every sane guide out there suggests - if (for iptables) you start with DROP on INPUT and FORWARD chains and gradually open what's necessary.