I too consider this a footgun.

Most applications will have something like

   tracing_subscriber::registry()
           .with(
               tracing_subscriber::EnvFilter::try_from_default_env()
                   .unwrap_or_else(|_| "my_app=info".into()),
           )
           .with(tracing_subscriber::fmt::layer())
           .init();

in the `main.rs` which will default the tracing if RUST_LOG env var is not set.