Eh, I don't see that as a downside. And actually, I'm not sure that's even true. It's already apparent that a lot of people are using a lot of completely unnecessary allocation in Rust, precisely because they aren't thinking about what they're doing (and so are doing things like using heap-allocated String objects when they really just need &str slices, or using Box unnecessarily; this was one of the reason cited for moving away from the ~ sigil, as it was considered to "hide" allocation too much).

And speaking personally, I almost never have to consciously think about allocation, unless I'm doing really performance-sensitive work. The straightforward approach is usually correct.