No, you can allow access to specific domains, IP addresses, filesystem paths, environment variables, etc, while denying everything else by default. You can for instance allow access to only a specific IP (e.g. `deno run --allow-net='127.0.0.1' main.ts`), while implicitly blocking every other IP.
What the commenter is complaining about is the fact that Deno doesn't check which IP address a domain name actually resolves to using DNS resolution. So if you explicitly deny '1.1.1.1', and the script you're running fetches from a domain with an A record pointing to '1.1.1.1', Deno will allow it.
In practice, I usually use allow lists rather than deny lists, because I very rarely have an exhaustive list on hand of every IP address or domain I'm expecting a rogue script to attempt to access.