That's not the point. The point is, if you do network I/O, you are processing untrusted packets from the internet. If a carefully crafted set of such packets can trigger, say, a buffer overflow, you're toast.
A first line of defence is authentication. Make sure the packets come from a trusted source (you can MAC each packet for this), so only those trusted sources could possibly trigger the vulnerability.
If the only trusted source is an authoritative server, you might be able to hide that buffer overflow. If your network code is peer to peer however, you have to trust the other players not to run a cheat that takes over your machine… but at least that's not the whole internet.
A first line of defence is authentication. Make sure the packets come from a trusted source (you can MAC each packet for this), so only those trusted sources could possibly trigger the vulnerability.
If the only trusted source is an authoritative server, you might be able to hide that buffer overflow. If your network code is peer to peer however, you have to trust the other players not to run a cheat that takes over your machine… but at least that's not the whole internet.