How could/would the language know when you can and can't afford it? Default semantics can't be "copying" because in Rust copying means something very explicit that in C++ would map to `is_trivially_copyable`. The default can't be that because Rust isn't trying to position as an alternative for scripting languages (even though in practice it does appear to be happening) - it's remarkable that people accept C++'s "clone everything by default" approach but I suspect that's more around legacy & people learning to kind of make it work. BTW in C++ you have references everywhere, it just doesn't force you to be explicit (i.e. void foo(const Foo&) and void foo(Foo) and void foo(Foo&) all accepts an instance of Foo at the call site even though very different things happen).

But basically you're argument boils down to "I'd like Rust without the parts that make it Rust" and I'm not sure how to square that circle.