Strong -1 on requiring an explicit action and/or dialog. I think requiring any decision is super beginner unfriendly. And deciding on bin vs lib is particularly difficult, because not every language has this distinction.
From my personal experience with project creation wizards, I've recently tried to play with OCaml, and oasis quickstart was suuuuper confusing to me.
A number of times I have deleted and recreated projects because of this mistake.
Hm, perhaps this is the problem we should target? It's better to provide an undo button than to ask for conformation. And it seems to me that switching between bin and lib is simple at the moment (rm src/main.rs && touch src/lib.rs) ?