Dropbox has lost my files as well. I had kept some very important private files there which I just wanted to keep there without the need of updating them/syncing them. After uploading, I removed the local copy of that private top level folder, as I didn't want to keep a local copy in my computer. With the next sync, this STUPID SH*T removed the folder from their server as well, without any warning of any sort! Any system which deletes the files without asking, should just not be used or depended on.
It sounds like you don't quite understand how Dropbox is supposed to work - it replicates whatever you have locally to the cloud and back down to your other machines. Obviously with a design like that, deleting files from your local dropbox would delete them from other machines.
This isn't a case of dropbox losing your files, it's a case of you not understanding how the tool was designed and how it works.
Many sync software offer multiple types of sync (e.g. MS SyncToy), and many are extremely cautious before deleting multiple files. Dropbox didn't do that. Yes, I failed to totally understand how did it work, as I deleted one of the root level folders and expected it'd not sync a folder which is not there on the local machine, but one of the duties of software is to prevent or try to reduce common human errors.
You deleted the folder, and dropbox synced the deletion. This is expected behaviour. I don't know why you entrusted crucial private files to a service you didn't fully understand.
