Would you not feel even slightly unhappy that your children (or grandchildren) would not be able to read the original versions of Shakespeare, Dickens, or Austen or that they wouldn't be able to watch the original versions of movies and shows you've enjoyed? They would only be able to watch and read translations, and all of the linguistic artistry would be lost to them.

It's not just about becoming bilingual, a population becoming bilingual in a "prestige language" is the first stage of language death (though of course it doesn't /always/ lead to language death).

No not really. English has shifted so far that those works are hardly as understandable now as a modern translated work.

That isn't the case for every language, I'm just trying to come up with an equivalent explanation of why wishing for languages to die out is a bad thing.