RAID arrays are not always used for speed. They can be used for:
To make the loss of data happen less often. This is done by having several copies of the data.
To get more storage space by having many smaller disks.
To get more flexibility (Disks can be changed or added while the system keeps running)
To get the data more quickly.
So again, in response to:
Raid setups are always less safe!
I say:
Depending on the RAID level used a RAID array can be dramatically safer than independent disks.
In the "mirroring" mode, dont you lose space and speed? Whats the difference between having that and a backup hdd?