The requiring a click part is the only relevant implementation detail for this functionality, in my opinion. Whether or not it requires a plugin shouldn't matter.
In fact, requiring a plugin for this functionality only serves to increase the attack surface for the browser as a platform.
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Imagine a web where you could just write to the users clipboard without a plugin + requiring a click.
It would NEVER be safe to Ctrl+V again!
The requiring a click part is the only relevant implementation detail for this functionality, in my opinion. Whether or not it requires a plugin shouldn't matter.
In fact, requiring a plugin for this functionality only serves to increase the attack surface for the browser as a platform.