It's not any of their business anyway.

If things that make me unhappy aren't my business, what is my business?

But whether your existence makes me unhappy or not, you are, of course, free not to care.
And even if you do care, you're not obligated to alleviate my unhappiness. You might care, and decide to make me more unhappy, for whatever reasons.

And, sure, we can try to kill each other as a consequence of all that.
It's not clear to me what ethical question this resolves, though.