The only flaw with Esperanto is that it is a language. Languages hate staying still unless they're dead. I say this as someone who spent several months studying

The only flaw with Esperanto is that it is a language. Languages hate staying still unless they're dead. I say this as someone who spent several months studying Esperanto and holding a few conversations. :) I treated it more as a "springboard" to language learning. Learning a second language is tough - learning a third language less so! So picking an easy second language, I found, helped speed up language acquisition (which was my goal). Languages naturally change over time as the population invents slangs and irregulars, typically out of laziness. Certain vowels will be mixed or slurred, parts of words might change entirely, etc. Even if Esperanto was taught to every individual as a second language - various regions would invent their own slangs based on the "native language of the region". Borrowing loanwords from their parent language and creating various dialects of Esperanto that may or may not be understandable with other dialects to varying degrees. I highly recommend learning Esperanto to anyone interested in learning a second language - to use it as a springboard to your third.