> The key problem has been that the resulting programs are fantastically hard to understand. One of the things I think Dijkstra got right in "Goto Considered Harmful" is that humans can reason about programs better when there's a strong correspondence between the textual structure of the code and its execution structure at runtime.

This resonates very strongly with me. I've been doing a whole bunch of side/toy projects in Rust for months, and I can attest that even compile-time metaprogramming can make programs "fantastically hard to understand". Runtime metaprogramming makes that problem an order of magnitude worse.

Don't get me wrong, I'm not against metaprogramming, either compile-time or runtime. But it's way too easy to get overly enthusiastic when doing it.