It seems appropriate that awarding one Fanatic badge should erase 3 Enthusiast badges earned in the same period. If it's already so, please close.
This is never the case with any of the badges. Enthusiast can only be earned once, so you don't get three on the way to Fanatic, but it makes sense to leave the one you had. For a much simpler example, if you post a question that gets 100 score, you'll get Nice question, Good question, and Great question; the previous one isn't revoked as you get the next one, it just means you've earned both.
There's a general rule that you never lose a badge once you've gotten it, even if you no longer meet the criteria for it, so losing badges you do meet the criteria for would be massively confusing