Just because you have a garbage collector doesn't mean you don't have to worry about memory management. I've see too many problems pop up because people don't understand how memory is managed in their GC'd language.
This isn’t true, in all languages with one you can ignore the garbage collector and still get work done. It may not be the most efficient but you still get work done. Let’s get a fresh out of code bootcamp grad in here and throw two languages in front of them if you want to test this.
You may be able to get work done, but I've seen actual bugs because people didn't understand how memory was managed. For example, not realizing that passing an object to a function was passing a reference, and not a copy. These are things that are explicit in Rust.
This won't result in any security related bug, you'd be updating the referenced version instead of a copied version. Both testing and use of the written code will show this "bug" if it's in fact a bug for this specific codebase. So now the question is, does rusts difficult learning curve warrant removing this "maybe" bug? There are other things to consider as well, memory fragmentation, performance etc. Have you measured the performance of code that both copies and updates?