With the default single-click setting, selection markers are practically mandatory, since without them there is no way to select files with the mouse.

But if you change the setting to double-click, they become useless annoyances: clicking anywhere on an icon selects it, so there's no need for a tiny hover button in the corner to provide this feature.

Plasma's Folder View shows and hides the selection markers automatically based on this setting; we should do the same in Dolphin.