Proprietary software doesn't give you the freedom to read and modify the source code. The software license forbids learning about it.
>one can't expect CS students to have an education which is valid for the workforce without any exposure to proprietary software at all
There's a lot more to CS than learning to be a code monkey.
This is true. However, it is still possible to be taught to code on a Windows machine in Visual Studio, or in Java for Android, etc. Your point of view has merit but it also has a limited context. The tools do matter and some of those tools are closed-source.
>There's a lot more to CS than learning to be a code monkey.
And yet, sooner or later everyone has to eat.
It doesn't allow users/students to analyse, or learn about, its inner-workings. I don't know how important that is but with git being so easy to deploy, why not use something students can maintain?
Sometimes it's best to start with something that transparently "just works", make the students aware of other options like gitlab, and let them explore those if they wish.
How to stage and sequence the exposure to the details is indeed important. I am not advocating exposure to the details right away, but the option has to be available at a reasonable price (be it in money, or in time).
There is also the "teach a person to fish" thing, rather than handing him/her a fish. Although many are in the business of handing out fishes, stale ones too.
No one argues that you need to have people host their own web server to start learning how to write Javascript. In fact, most would argue against hosting your own that early on. It's not beneficial, and more likely to end up tangential annoyances than solving the problems that matter for the person's skill level.
Just because someone teaches you a different part of the stack first doesn't mean they are handing out fish...
At the very least, one can't expect CS students to have an education which is valid for the workforce without any exposure to proprietary software at all.