If you look at the conversion rates from the available subscription costs into the yen (JPY) it is as follows:
1480 JPY is the standard 30 day subscription fee for Japan.
(taken from here:
http://jp.finalfantasyxiv.com/pr/product/)
8.99 GBP = 1417.97 JPY
12.99 EUR =
1731.90 JPY
14.99 USD = 1502.60 JPY
(taken from current conversion rates, I'm aware it will fluctuate)
It becomes quite apparent why they would go out of their way to make as many people to pay in Euros as possible. While GBP and USD are reasonably close to the monthly JPY subscription cost, everyone else using the Euro is paying more to play a month.
So not only on top of the higher conversion cost from currencies like the AUD, NZD and SGD to the EUR, you are also being charged more per month to play the game than other people fortunate enough to be using an account that can pay in GBP or USD.
Is it ethical? I'm not sure it really depends on the reasoning behind the increased costs. Maybe it has to do with local taxes? But even so, it does seem like they've gone out of their way to try and get the subscription costs as close as possible for currencies other than the EUR.
Ultimately, I personally agree. If you're going to be made to pay in a currency that isn't your own, then you should be able to pick from those available so you can at least pick the cheapest to convert to.