I'd recommend this approach because no matter what you put into your list, you're going to miss a character, especially as new characters are added (who cared about € 14 years ago?) What happens if someone inserts Å? á? Ø? Æ? ð ? þ ? — ? „ ? Kanji? Mathematical symbols?
You're *much* better off listing the characters that you want to keep, and removing all others, if only because it's less work to maintain in the long run, as you don't have to worry about adding new characters, or if someone's messed up the encoding of the script.