My two cents: as a crowdsourced database, it's important for everyone to contribute while following the site's rules and guidelines as closely as possible. Not only does this make it less likely that someone looking for a card won't find it where it should be and then creating a duplicate checklist--it also means less work for the members who donate their time to the site adding checklists and resolving IRs.
If someone wanting something added to the site doesn't do a reasonable amount of research, that work falls to the IR resolvers, and that shouldn't happen. And while in some cases a card being in the wrong spot is easy enough to resolve, many times it becomes a big project, especially when a whole set's checklist is involved. Then you have to take into account images and collection info before you can delete the cards in a dupe checklist, then the extra set, and often that has to be done one card at a time. So I hope this clears up how multiple people doing this can snowball into a huge amount of time needed to fix mistakes.
It's also important to keep in mind that a number of members here are happy to help when you start a forum topic like this, but "help" won't always end in the card/checklist getting added the way you think, but instead the way it should be according to the rules here.
