Who said that? I could not agree less. Butterflies are beautiful for their color, not their death.

It's from "Sohrap Sepehri" [1] an Iranian poet and painter. and I think the replies to your comments answer you question.

[1] https://en.wikipedia.org/wiki/Sohrab_Sepehri

Whoever said that, probably meant selection pressure.

Potentially also that if every butterfly that ever existed were still alive, we wouldn't be very fond of them.