I agree with him. All software should be written in safe languages, but there is a wide selection available. For new projects you should pick a language that does as much for you as possible. Ruby and Rails both go out of their way to provide the developer with as much power as they can. They make development less expensive. That’s exactly what you want when you are first building something, before you know exactly what you will need.

Later after you have lots of users and your hosting costs are rising, then you can rewrite it in a language that gets you closer to the machine. You won’t need to do any exploration at that point, and you’ll already know where the performance hot spots are. Of course I recommend Rust for that, but that is merely my personal preference.