Re: all damage is combat damage effect. This would wreak havoc in commander. Take borborygmos enraged for example. "Discard a land, borbor seals 3 damage to an opponent" currently is not a great win condition, but if you made it all count as combat damage it would make it so if you filled your hand with lands and discarded 7, you would win by commander damage. There are quite a few effects like that and it could really upset balances.

It’s the kind of effect that could potentially break a number of things.

I feel like you misunderstood the question mark referring to the trolley problem (whom I totally agree with, btw). Emrakul was going to wreak havoc over any plane she moved to. The vampires didn't 'have it coming,' Nahiri just positioned the havoc in the place most likely to prove a point. Antagonists who don't need completely contorted reasoning to justify themselves I, personally, find much more compelling than, say, Voldemort, whose evil just stems from being evil.

My point was Nahiri took actions that are hard to justify as heroic and not that hard to call villainous. Imbedding the Vampires in the wall was to send a message to Sorin, not because those Vampires had done any wrong to her.

One thing I am confused about: Zendikar block. You make a plane that probably 95% or more of the Magic community loves. But then, you wreak havoc on the entire plan and practically nothing is left. How come?

Because that’s how story works. There has to be some conflict of some kind and since we tell stories at an environmental level, something has to happen to the environment.  Note that both Mirrodin and Ravnica had some radical change at the end of their respective blocks but we still managed to return to each.