Emojis are characters in the Unicode specification, which have glyphs in the macOS default font, and are rendered by default in native macOS apps that display text. Why should Emacs make the decision that most characters are okay to display in their text editor, but these specific characters are a no-no?

You're sounding like "I'm not using this feature, why does it even exist?". If things worked like that, then everybody would be using Linux on all computers today.

And therefore nobody else should be allowed to have them either. Which is the explicit justification given for this decision. Sheesh.

Then don't put them there, or install an alternate font.

"my" is the key word there...

Your argument sounds like "A man shouldn't be allowed to marry a man because I don't want to marry a man"