I love it when fanartists kind of compare fanart to the Bible, kind of missing the mark of why Monks where making all that Biblical art in the first place. For them it was a communion with God--a literal type of worship. They literally worshiped the icons that they made. But artists make fanart nowadays to say "I like this" and...get internet followers for social media websites that probably won't exist in like 10 years. It's totally different.
And like, fanart isn't bad to do (and to sell, you just have to check in with the creator to see what they do and don't allow. Many allow sales of things for artist alleys and etc. But, if you're ever asked to take something down. Take it down without a fight.) But there's no need to make it into this glorified, transcendent, noble experience like you're Robin Hood giving money back to the poor. You aren't a monk working in the Church of Naruto and painting your beautiful Naruto portrait after a long morning of fasting and prayer. You are making that Naruto peice because I guess you like Naruto. And that's fine.
Now there are instances where fan translations have saved art that couldn't be saved in any other form--so for instance video games have a lot of platforms that have died, and so you'll have these ancient games that only came out in Japanese, that you cannot play at all, and can only be accessed through an emulator. In this case, the fan translation of these games helps to keep it in a library of sorts so that the game doesn't disappear entirely (so in the case of Snatcher, for instance, which for a while was hard to find.)
But in the case of comic books--these are probably not going to disappear since paper is...paper. If the rarity of the comic really is "wow there's only 5 of these on Earth and we have to save it or it will disappear" then that is a different story. But it's just rarely ever the story.