There's nothing wrong with logging to a database, provided you adequately buffer the insertions to keep the underlying sync() rate reasonable.
I wouldn't recommend logging to the same database instance that's used to store customer data for both security and performance reasons, but that's no reason not to use a database for logging.
I agree, what it should say is: never log to the main database, create a DB especially for it (preferably in an entire different file system/disk/machine)
I wouldn't recommend logging to the same database instance that's used to store customer data for both security and performance reasons, but that's no reason not to use a database for logging.