During various VDG discussions at Akademy, there was general agreement that the Translucency effect shouldn't be on by default. Entirely putting aside arguments based on aesthetics (which are subjective) and "datedness" (which are not usually appropriate since following UI fashions rarely bears fruit), there was a galvanizing event during this Akademy that revealed a very convincing new argument: privacy. Someone was giving a presentation during the KDE e.V. meeting and resized a Dolphin window to make it bigger. The act of doing this revealed the content of the window beneath it. This could have been a very significant privacy violation, depending on what content was under there. It is not at all inconceivable that one could accidentally reveal trade secrets or expose oneself to personal embarrassment in the process of trying to avoid just those outcomes, because the entire window becomes translucent if you try to reposition or expand it to conceal what's beneath. This effect does not seem to fit well with KDE's goal to focus on privacy. As such, I believe it makes sense to turn it off by default.