I'm in love with Ubuntu, but I really HATE this feature. I am a programmer and it happened a number of times that I introduced a bug because I inadvertently pasted some code which didn't belong there. I still have nightmares from debugging.
And I can't even turn it off in the 'Mouse and Touchpad' window.
I think it's a weird design decision. Most people expect the middle mouse button to map to scrolling. What was the rationale behind this decision?