After all these years, why is it that pundits still associate use of VLANs with security? Any security afforded by use of a VLAN is a side effect and is considered (by those in security) as not assurable (e.g., it cannot be proven by testing), is easily broken, and is very easily mis-configured.
A VLAN is a traffic management tool, designed to increase overall (employable) bandwidth in an architecture. It does not employ authentication or encryption. Security is increased (often negligibly) by ensuring that traffic doesn't "go" somewhere. In some architectures (e.g., VoIP phones on the same network segments as the workstations), this separation doesn't exist.