RAID1 is never to be considered a backup. Mirroring is instant - that means any corruption, damage or problem instantly also involves the mirror drive. RAID1 does not add data security - it adds uptime in the event of a drive failure (hopefully, if it works right)
The only thing that gives data security is a second discreet copy - a backup. That copy should be maintained by virtue of a backup utility. As such it is disconnected from the main data drive except when the backup utility is updating it. Should any catastrophic event occur your backup drive is hopefully not part of the problem.
A proper NAS is really a computer with shared storage. Most cheap NAS units today are a simple hard drive with a network bridge attached to it. They work ok except they do not have a way to manage the data nor run a good backup. Most of the cheapies also do not do the minimum required of a storage enclosure: maintain stable voltage and maintain stable drive temperature. Those little brick power supplies are insufficient to the task of a stable voltage output to the drive, and the lack of decent cooling is the other cause of higher drive and component failures. SIgnificantly higher failure rates. There is no substitute for a quality internal power supply and active cooling when it comes to drive longevity. All of which increases data security.
Quality NAS units, those costing upwards of a thousand dollars (without the drives!), have an onboard motherboard/dedicated processing unit to manage the storage, share it over the network, run backups and maintain the database free of corruption.
I half agree with you, in that a RAID1 doesn’t protect you from data infection or corruption.
What it protects you from is a hardware failure. The question is whether you think most of your data loss will be due to corruption, or hardware problems.