Pretty sure that's unsafe, don't do that.

Only the scratch buffer is to be exempted, not every buffer that gets this mode.

Do note that I only configure this for `lisp-interaction-mode', which in practice really only gets used for the *scratch* buffer. But there are a few other instances in core that also use it, and if that concerns you, you can extend the above snippet with a check like

    (when (equal (buffer-name) "*scratch*") ...)

Agree. This is probably better:

    (with-current-buffer "*scratch*"
  (setq-local trusted-content :all))

In practice this should also work. Do keep in mind if you just add this to your init.el then this will not persist if you re-create the scratch buffer.

If we are already experimenting with different ideas, this should also work (and gives a hint of how you want to fix the issue upstream):

    (define-advice get-scratch-buffer-create (:filter-return (buf) trusted)
      (with-current-buffer buf
        (setq-local trusted-content :all))
      buf)