In the same post you are arguing for and against "slippery slope".

Either it is possible to easy change law to make it worse ("slippery slope" is valid objection) or changing law is "much harder than doing nothing"("slippery slope" is a fallacy).

The thing is you don't need to do this in "normal" system where dependencies are stored in local cache and build tool is using them during the tasks.

If JS had a proper build tool then creating such directory inside project would not be needed. Instead in JS world you have only dependency downloader with some crude script runner.

You still need to have those symlinks checked. For example you switch branch to one with updated package.json, now you need either to check symlinks or you risk to have incorrect build.

Introducing a directory that needs to stay in sync with dependency manifest will always lead to such problems. It is good that Python developers do not want to repeat such mistake.

This is literally not possible.

If you have local dependency repo and dependency manifest, during the build, you can either:

1. Check if local repo is in sync - correct build, takes more time

2. Skip the check - risky build, but fast

If the dependencies are only in the cache directory, you can have both - correct and fast builds.

It is possible to set version ranges but it is hard to see this in real world. Everyone is using pinned dependencies.

Version ranges are really bad idea which we can see in NPM.