The point is that they can still. Whatever the standard for taking time off work for illness it should apply equally to both genders so there should never be any need for a separate rule/law.
Not sure those optimisations are worth much. And it's only safety by forcing lowest common denominator code and making you justify everything to a dumb compiler. Rust serves a niche, but it is a tight niche IMO.
Your "solution" is possible in many languages. It's just to give threads complete ownership of data they use. It doesn't require a special type system.
In general I don't think Rust actually adds much abstraction that isn't already in say Python. What it does is enforce tight constraints.
Not my area of expertise and it is yours, but if you eliminate a zero instruction before a copy instruction how can you be sure that doesn't affect other threads?
var x Int
// Pass x to a thread by reference
x = 0
time.Sleep(1000)
x = 1