It's weird how some of the same people who use middle-click-to-paste also use password managers (which are a good thing).
If that's you, then you're quite daring when you're using collaborative apps (that have history!)
I agree with everyone who says middle-click-to-paste really should be off by default.
It's actively harmful and can easily paste sensitive information and surprising clipboard contents.
(Anyone who likes it is advanced enough to figure out how how to turn it back on.)