Plasma's Task manager exposes an optional feature whereby the user
can middle-click on a window to close it, but the Present Windows effect
does not do the same.
The presence of a close button you can left-click does not replace the desirable
feature to be able to middle-click on a window to close it, because then the
whole window becomes a click target, so it can be much much faster than
having to aim for the little close button. Also it's off by default, so a user
who goes out of their way to turn it on is signaling that they want to accept the
risk of accidentally closing a window by accident.
Finally, the feature is not allowed for left-click, so people can never accidentally
wreck Present Windows for themselves by assigning it to left-click by accident
and then mistakenly closing their windows.
This reverts commit 55585514f926d1251148e876bfe9ce3504432997.