Make double-click the default
Now, I know that most of you will immediately take the reflex of closing this merge request because "oh my it's yet another make it double click patch", but please hear me out before you go to make that reflex.
The case for double-click as default
As you may already know, Plasma is in the very small minority of desktop-oriented desktops that have single-click by default. It has become a culture over time for Plasma, potentially, even to have single-click.
But there is one problem with that - the fact Plasma is in a very small minority. Pretty much more than 90% of commonly used desktop environments and basically ALL the leading competition on the desktop market use double-click by default. This creates a problem for people seeking Plasma as they are used to the double-click behaviour, and so get easily frustrated when trying to do basic tasks (such as changing their current selection to be selecting a different file or folder) that would work on double-click that instead cause files and folders to be opened on single-click.
That being said, I feel that it is for the better to make double-click the default. But I'm not done explaining just yet.
What about single-clickers?
Here goes another point to further this. Users expect double-click on desktops because of their knowledge of behaviour in macOS and Windows... except for the people that prefer single-click.
Those who prefer single-click very likely, if not do, know about the ability to switch between single-click and double-click. That sets them apart from users who expect the behaviour of double-click out of the box in a desktop environment as they very likely DO NOT know of such a setting even existing.
That being said, if we go to double-click those unknowing users will get the behaviour THEY expect, while single-clickers can go back to single-click using the option that they know about and be on their merry way once more.
The case of Plasma distributors
This isn't really a point per-se, but I thought I should mention this regardless. Popular Plasma distributions such as Kubuntu change the behaviour to double-click by default for reasons that are very likely justified, usually including the points I've already made above.
If even the distributors are changing our default of single-clicking to double-clicking, doesn't that say a bunch about our default choice of single-clicking?
Finally, to end this initial merge request message, I'd like to finally cover something that is very likely going to be a roadblock for this merge request if not acknowledged: Inappropriate application behaviours relating to this setting.
The main thing that comes to mind with this topic is System Settings's icon view. That view follows double-click behaviour if on, when really it should enforce single-click because single-click there is an expectation in itself for most people. Windows Control Panel (and 'Settings'), macOS Settings, heck even Plasma's own sidebar view all follow single-click irregardless of if double-click is enabled or not.
I won't mind if we keep this patch delayed until these inappropriate behaviours in applications are fixed, but we ought to get these inappropriate behaviours fixed in separate patches to resolve any potential qualms in all these applications related to making double-click the default.
What about Plasma Mobile?
I'm sure that for Plasma Mobile an exception could possibly be made to make that platform use single-click by default (or maybe make single-click the default only when in 'tablet mode'), but that's besides the point of this merge request.
In conclusion, this patch all comes down to user expectations with how their desktop behaves. Maybe this pull request will be doomed to fail just like other times people have suggested double-click by default, but it's worth a shot irregardless of that fact.