This is not at all comparable to FF. Because FF gives you rating in super casual content, here it is about being helpful and terribly bad.
M+ is much more endgame. If you wanted to add a friendly player system in heroics or m, I'm all for it, just not in m+.
Also funny, that you mention "evil strawman", when this is the entire point of this thread. VERY few people leave maliciously. I'd argue this are so few people, that it would be ridiculous to change the game due to them.
People mostly have areason to leave. I have done close to 300 keys this expansion, and I have yet to see people leave maliciously.
Most of the time, they just leave after it is a certain deplete, or the key is becoming unfun, due to many many mistakes.