Depending on the underlying storage being reliable is far from unique to garage. This is what most other services do too, unless we're talking about something like Ceph which manages the physical storage itself.

Standard filesystems such as ext4 and xfs don't have data checksumming, so you'll have to rely on another layer to provide integrity. Regardless, that's not garage's job imo. It's good that they're keeping their design simple and focus their resources on implementing the S3 spec.