Yes
Yes.... why should she care about the world did the world cared for her?
If that world ends, she would die too...in the body of Ishana
Adding to your point, whilst it is asshole behaviour him threatening her, I don't think that was his original plan. He probably wanted to convince her to marry him more slowly, but her revealing her powers is what made him feel like he had to rush the marriage which is what lead to the threatening, because otherwise, she may try to run away to escape people's scrutiny and if he loses her, he'll eventually go kaboom and he can't afford that. He was definitely in the wrong, but as the emperor he's always going to trying to do whatever best for his people and he obviously don't want to end up killing everyone so he's going to do whatever it takes, even if its wrong. He's not a bad guy, just an emperor he will do whatever it takes to protect his people, even at the expense of others.At the end of the day,just blame the author for using such a trope, its clearly overused and unrealistic and people are just sick of it.
To those who hates the Emperor for threatening the FL.
1. Have you guys ever had a thought why he threatened MC?
Ans. She refused to marry him.
2. Why does he wants to marry her?
Ans. Because she's a witch and she can hold/control the curse in the Emperor's body.
3. Why does she has too?
Ans. Because he already feel like his body won't be able to contain the curse longer.
4. What happens if the curse explodes?
Ans. Their world would explode and many people would die.
I agree that it is wrong for him to threaten, but is it still so bad so when he was thinking of the greater good? Is he still an a-hole for that?