I don't think this is true at all. Reducing copies and allocations in my programs is one of the things which has speeded them up the most.
> If widely useful data is protected by the borrow checker, far fewer people will use it.
Are you also against private struct/class fields? Because they also restrict access to useful data.
For me, the need for Rust is as a language that gives me maximum possible performance, while giving me safety guards that C and C++ do not. This makes Rust much easier to use than those languages for me.