I would just like to clear this up: I do not support the notion of any universal language, and that includes English. My observation that English is relatively more universal than Esperanto is not an endorsement of the premise of universal languages being a laudable goal.
But it would have to be grassroots - if the English government mandated that everyone speak Esperanto in school then tried to spread it round Ireland and the EU it would ruin it. Same if the EU adopted it en masse, Brexiteers would reject it on principle. It could only ever happen if it grew in a balanced way where more and more places distributed around the world use it, and more and more people around the world learn it because it’s useful, and it somehow never becomes one country or one group’s unfair advantage. (That is to say, it can’t ever happen).
Would you still oppose a universal language if it was voluntary, not pushed by one nation into others, and not a replacement to primary national languages?
It’s an idea that can only really succeed from a combined goodwill not conquering oppression.
All over Europe there isn’t room to put up road signs and menus and instructions in the union of all possible languages visitors could speak. It’s easy to say all visitors must learn the local language, but there’s often some concession to putting up signs in some other languages, Esperanto fits there. All road signs seconded in Esperanto isn’t as good for locals as all visitors learning the local language, it isn’t as good for visitors as signs being in their native language, but it isn’t as bad for locals as one group of visitors expecting signs in their language and it isn’t as bad for visitors as signs being in multiple native languages but not theirs.
Expecting to go anywhere and speak English is rude. Expecting everyone to learn English is unlikely and going to trigger a lot of anger. Also supporting French shows some openness but privileges France in a national way. If you could get language away from nationalism, tourist information in Esperanto doesn’t privilege any one nation.