If you as a reader need const to make sure a local variable is not changed this is usually a symptom of this function being too long to see at a glance. And quite often as code changes I do need to make some local variable non-const, and it quickly becomes annoying to fiddle back and forth enforcing const-ness of every local variable.

The argument about optimization is almost certainly premature optimization. Most of the time how you write a loop doesn't matter. You only find out what matters via profiling and refactor accordingly.