People with only one vision or less (0).
People that can only see one thing or in most cases lacking vision completely.
A "onevision" therefore steal visions from others in most cases.
A "onevision" can also be called a "novision".
Picture of a "onevision" character:
"What a onevision!"
Meaning: what a stiff vision lacking piece of shit moron,
One of those vision lacking thief's.