I cannot think of a single POSSIBLE disadvantage to having Unicode support on the forum. None that would justify it's removal.
ASCII is as basic of an encoding scheme as it gets, designed to be the minimal required standard for character translation from machine to machine.
I think there have to still be some EEs not working in English. Whether that is true or not is a matter of subjection, and the fact that with a pool of 7.6 billion people, and 1.5 billion English speakers, there has to be one person in that 5.1 billion excess that is a capable, functioning EE. Regardless, this forum isn't always about EE. Current issues relating to tech, and people in general is often brought up here. Strange product names in other languages, or someone asking for a quick translation of some text might pop up. The point isn't, if there isn't an immediate apparent to me, a single user, it should be ripped out, is not an adequate reason for not having Unicode support.