People also used to program computers with punch-cards. Everyday. Of course they can use Javascript.
You didn't address any of his points though. Where are the great Javascript tools and IDEs? There are tons of them for languages with static typing and classical inheritance.
Here's just one tiny example: Compare how you go about refactoring code (renaming classes, functions, etc) in Javascript with the many ways that it may be done in Java or C#.
He made many points, Javascript not having great tools and IDE's is only one of them.
It's a valid one though, the Javascript IDE's out there aren't very good. However, that's a function of community support, not language quality. Personally, I don't use an IDE for javascript or RoR programming, I just use Textmate.
I use Eclipse for Java programming, and I don't think I would want to program in Java without it. Maybe it says something about the languages themselves that they require an IDE to develop in.
Actually, many people have tried to build refactoring and editing tools for JS and they always hit the same limitations. The language is just not conducive to tooling. Without a great refactoring tool, big projects become difficult.
You didn't address any of his points though. Where are the great Javascript tools and IDEs? There are tons of them for languages with static typing and classical inheritance.
Here's just one tiny example: Compare how you go about refactoring code (renaming classes, functions, etc) in Javascript with the many ways that it may be done in Java or C#.