I disagree. I'd argue that a monolingual species is harmful for the same reason monocultures are harmful in general.
Language diversity facilitates cultural diversity. It's a "memetic speed bump" that enables the isolation needed for cultural divergence.
On a hundred-year timescale, I'd much rather see hundreds of new, diverse cultures bloom than some sort of bland Facebook-y monoculture where everyone is communicating with everyone else all the time. I'm hoping in the very long run, space travel will help facilitate cultural diversity. E.g. Mars is ~10 light-minutes away, meaning Earth/Mars phone calls aren't really feasible. But until then, we should preserve the cultural diversity we have, and fight homogenization.
It is in some ways a bit peculiar, with a simple grammar but extensive vocabulary (much of which thieved from other languages). It is on the face of it quite ugly, however great poetry and works of literature have been created using it. Some non-native speakers say they feel freer using English instead of their native tongue, but of course that is a somewhat nebulous proposition hard to substantiate, even if there is a little truth to it.
I suppose there's still the issue of inconsistent phonetics when reading an unfamiliar word...
Many of the French words came about due to England being invaded by he Norman French. A lot of food words come about due to using the native terms for those -- this is why the meat words are French based and the animal words are Norse/Germanic.
In Florida, you see a lot of Spanish words entering English due to the cultures co-existing and mixing. This happends a lot near country borders where you see languages blend together as the different speakers mix.
Do creole languages (of which there are many) steal the words from their parent languages?
Probably why technical term is loanword :)
... it's not like the word gets used up in the original language [1]
Humans are way too clever and adaptable to receive and reify one language and will always be tuning in to accidental quirks and personal optimizations. There will always be many languages, some old and some new, because people will always live within the practical little social bubbles that get them from today to tomorrow.
On a funny side note, I recently overheard one Spanish speaker casually comment to another about how people's personalities seem to change when they switch which language they're speaking. It was wild to see someone who's never heard of that hypothesis just invent all on their own.