Earnest enthusiasts often declare that the existence of Esperanto websites proves that it's a living language; but they're wrong – it isn't, and if they had any sense they'd be happy about that.
The reason they're so keen to make this claim seems to be that they've heard that living languages inevitably evolve over time. Hurrah, they think: we can stop pretending that Esperanto is perfect and switch instead to claiming its flaws will naturally dissolve away! Unfortunately, Esperanto isn't changing the way living languages do, and needs the kind of systematic redesign that natural language change can't provide.
A “living language” isn't just “a language used by living people” – after all, people still use Latin (and various similar dead liturgical languages). A living language is one with a viable community of native speakers using it as their primary medium of communication in everyday life, including bringing up their own children in it. If it stops being passed on from generation to generation, the language becomes moribund and eventually dead; but that's not something that has ever really started for Esperanto. Yes, it's true that Esperanto has had mother‐tongue speakers, but those denaskuloj have never formed the sort of native‐speaker community that naturally assumes control of the development of the language. On the contrary, almost all of them go on to raise families in some other language, while new speakers continue to learn Esperanto as a foreign language from courses based on the sacrosanct Zamenhofian ruleset.
But these facts shouldn't make Esperantists unhappy, because being a “living language” isn't a status that a constructed lingua franca necessarily needs to aspire to in the first place. Some of the most successful languages in history have been dead ones! Living languages are defined by the way their native speakers use them, so they continually mutate and diversify, and foreign learners simply have to put up with that. But being dead, Latin had the advantage that two people in different countries who had learned it from timeworn textbooks could communicate on more or less equal terms; there was no privileged population of speakers using it as their mother tongue, and as a result it didn't inconveniently change from decade to decade. Perfect!
(As long as they stuck to writing, anyway. Until the late nineteenth century there used to be multiple competing traditions in reading Latin, none of them very close to the authentic classical pronunciation*; so a word like circuitus = “a going‐round, a circuit” would be pronounced [tʃirˈkuitus] by the Pope and [tsɨrˈkvitus] by a Russian academic. Borrowings like Esperanto's cirkvito = “a circuit” were taken from the Eastern European regional standard just as that standard died out!)
Meanwhile, a lot of people seem convinced that the mark of a successful constructed international auxiliary language is that people use it for all sorts of highbrow purposes – this being, after all, the tactic that European ethnic minorities such as the Welsh have traditionally adopted to persuade their foreign overlords of how deserving of respect their ethnic language is. But it seems to me that Esperantists are missing the point of the exercise, which is to show outsiders that even if they don't recognise Welsh as precious for any other reason, there are cultural treasures that they'd lose access to if the speech community withered away. Esperanto doesn't have a National Eisteddfod, and hasn't had a millions‐strong population of first‐language speakers for the many generations it takes to generate that sort of literary heritage. If you produce an Esperanto equivalent of the Mabinogion, congratulations, but you're writing in a non‐native language for an audience who are reading in a non‐native language, and who wouldn't be appreciably worse off with a good translation.
Global auxiliary languages are supposed to be valuable for an entirely different reason: as a bridge between communities isolated by language barriers. They present the hope that everybody in the world can have access to all of those hoarded treasures, if only in translation. The idea isn't to tempt those communities to emigrate permanently onto the bridge by building an amusement arcade there! Quite aside from the disastrous consequences this would have for the survival chances of languages like Welsh, it's a sign that Esperantists have lost track of the original goals of the international language movement. A successful worldwide lingua franca isn't something that a few zealots use for fancy intellectual pursuits; it's something that billions of people learn at school, and regard as dull but practical.