It's clear from the conversation in T7928 that this needs more discussion. Let's do it here:
Advantages of status quo (single-click to open)
- Makes opening files and folders much easier for users with poor dexterity or mousing skills, laptop trackpads, and touchscreens in particular (where double-clicking is practically impossible).
- More intuitive; many users on other platforms have never fully understood when they need to double-click, and end up cringe-inducingly double-clicking everything "just to be safe."
- More consistent with mobile, where double-clicking doesn't exist. Vastly more touch-friendly.
Disadvantages of status quo
- Unfamiliarity for users migrating from all other desktop platforms, which all select with single click and open with double-click. We discard up to 30+ years of muscle memory.
- Makes selection much more difficult by reducing the click target to a tiny square in the corner. For touch users, it's literally impossible, since the selection marker only appears on hover, and there is no hover with touch.
- Makes multi-selection in file open dialogs infuriating, since no selection marker appears and there is no visible method to select multiple files.
- Makes file save dialogs confusing. Single-clicking on a file suddenly no longer opens it. Why? Not clear. The UX breaks down.
Let me mention that I actually really like the single-click setting. I just think it can't work without a lot of engineering effort put into resolving the above issues. Because right now, it's half-baked, halfhearted, and riddled with bugs. If someone proposed it in a patch today, we would block it on the above-mentioned objections, and possibly more.
If we're going to keep the feature used by default, then we need to make it work properly, and resolve the UX issues I detailed above. Mobile OSs that implement single-click-to-open (as well as GNOME apps) typically expose a dedicated "selection mode" that's invoked by pressing a "select" or "edit" button, and while in that mode, buttons for cut copy, paste, delete, and other contextually-appropriate actions become visible. If we're going to stay down this path, we need to be all in; the tiny little green selection button in the corner is not sufficient. We need to do serious usability and engineering work to accommodate common workflows in single-click mode vastly better than we do now.
If we aren't willing to do that or lack the resources, then we should consider it an experimental feature and not have it on by default, and not break people's muscle memory and experience for the sake of exposing them to a buggy, half-baked UX.