Let's just do this the easy way and be blunt:

Violence should probably stop while the alicorns are nearby, for now.
Violence begets violence.

Alicorns are really good at violence.

Blackheart is making that point as clear as it can be possibly made right now.


They and the Goddess are very likely the single most powerful things in the Wasteland, but they're held back by their arrogance in that fact.
Generally, what that means, is to follow Twilight's advice: Be Smart.

Look at the action you're about to take, consider the consequences.
What happens if it succeeds? What happens if it fails?
Is the risk of what happens upon failure worth it?