If you're just worried about accidental drag & drop into sub-folders (e.g. while trying to click on things and you move the mouse a bit too far with the button down):
- Preferences / File Display / Mouse / Allow drag and drop into sub-folders
If you want a confirmation before drag & drops:
If you want to block drag & drops entirely, do the same as the previous item but delete the unwanted events entirely.
(Note that drag & drop event customisation may not affect special cases like FTP sites.)