Because it's the same code as the client, which is "where the users are." I guess you'd assert that having the same language on the client and server doesn't justify the cost of using the language.
Correct. This argument, IMO, is mainly made by programmers who are afraid of working in more than one language at once, traditionally .NET developers who are used to an entire, ready-made, tied-up-in-a-bow ecosystem being dropped on their doorstep. I have a lot of trouble sympathizing with that perspective (even though I've had multiple jobs as a full-time .NET developer).
JavaScript is not good. We should be working to get it out of the way, not converting everything in our environments to run on it.
JavaScript is not good. We should be working to get it out of the way, not converting everything in our environments to run on it.