> We are already accustomed to R, Python, Node, Ruby, etc. building C stuff at package installation time. I don't have a great sense of where to draw the line, but somehow I feel the Julia convention crosses it.

I'm definitely not accustomed to this, and absolutely hate this behavior. Very frequently installing a dependent package or compiling one via one of these package managers is frequently a good way to build it badly, without respecting compiler flags, ignoring system paths, and so on. It's also hard to customize or force the usage of a shared system library which has been built for the purpose.

Ask the package managers of any linux distro how annoying is to handle unbundling in these scenarios.

pip too.