This is one of the most useful things in Xorg, and prior to that in X11. If you (generic you, not anyone in particular here) don’t know about it it’s because you come from too long time on “my users are stupid” operating systems. It’s one of those things that once you have it in muscle memory you use it without even thinking about it.
Have I mis-pasted things? Yes. Have l pasted my password in an IRC channel? Yes. Would I stop using it because once every few months I make a mistake? Not at all.
Make it configurable, if you must, but leave us old timers work the way we have done for 30 years or more. There are already some software/ toolkits that disable it, so it is likely doable on a per-app basis.
Gratuitous “old man yells at clouds” rant: people should be forced to use a VT52 for one year before being granted GUI privileges, especially if you work with network hardware.
I’ll crawl back in my cave now.
It’s been some time… Before Xorg there was Xfree86, and before that the various implementations by the other Unix vendors. Does that make sense?