npm installs aren't the same as installing from a random URL, because:
* NPM (the org) guarantees that published versions of packages are immutable, and will never change in future. This is definitely not true for a random URL.
* NPM (the tool) stores a hash of the package in your package-lock.json, and installing via `npm ci` (which enforces the lockfile and never updates it in any case) guarantees that the package you get matches that hash.
Downloading from a random URL can return anything, at the whims of the owner, or anybody else who can successfully mitm your traffic. Installing a package via npm is the same only the very first time you ever install it. Once you've done that, and you're happy that the version you're using is safe, you have clear guarantees on future behaviour.
they know there is a bad mitm vector and won't fix it
It'd be interesting to look at ways to mitigate that by requiring anybody using a package version to rehost it for others (since they have a copy locally anyway, by definition). But then you're talking about some kind of IPFS server built into your package manager, which now needs to be always running, and this starts to get seriously complicated & practically challenging...
I don't detest NPM in the way that some people do, but I have always worried about the implications of the fact that nearly the entire community relies on their registry. If they ever fell over completely, they would have hamstrung a huge amount of the JS community.
If you want to "feel" as safe, you have import maps in deno, which works like package.json.
Overall, I think Deno is more secure because it cuts the man in the middle (npm) and you can make a npm mirror with low effort, a simple fork will do. Which means you can not only precisely pin which code you want, but also make sure nobody knows you use those packages either.
Take it with an open mind, a new "JSX" or async programming moment. People will hate it, then will start to see the value of this design down the road.