I don't see why people stick their noses up at eval chat extensions. The absolute worst thing you could do with eval is delete someone's add-ons or overwrite their key.dat. Once Truce created 100gb of text files in my config directory. Anyway, point being, it's hardly even a security hole. If you think that someone might forget with your Blockland directory, that user most likely shouldn't have Super Admin on your server.
This. There's only so much Blockland can do, due to both the engine and how Badspot has modified it. Its scope goes no further than its own files.
I do agree that you shouldn't use it just for fun, however. The only reason you should ever use eval (a highly protected, initially host-only permissions-based chat bound version in my case) is for when you're making a mod with someone else. I used it with Zeblote when making Trains and Super Creeper.