That will cause UX regressions in cases where text is selected by JS and you want to copy it, and leads to "this text is clearly selected but if I press middle

That will cause UX regressions in cases where text is selected by JS and you want to copy it, and leads to "this text is clearly selected but if I press middle click it pastes something else, wtf?!" kind of scenarios. You can consider that to be an acceptable trade-off, but it is a trade-off.