While not a noun, the term knee-jerk is often applied to the category descriptor to demonstrate blind allegiance
(Of a person) responding in an automatic and unthinking way: knee-jerk radicals
[ODO]
Possibly partisan
a person who takes the part of or strongly supports one side, party, or person; often, specif., an unreasoning, emotional adherent
[Collins]
The term chauvinist is also used to indicate fierce commitment to a cause or point of view
A person displaying excessive or prejudiced loyalty or support for a particular cause, group, or gender: what a male chauvinist that man is
[ODO]
When coupled with an aggressive, often militaristic stand, the term jingoist may be used
Extreme patriotism, especially in the form of aggressive or warlike foreign policy.
[ODO]