Let me give more proof: In one of the episodes of season one of the Legend of Korra, you can see a Chi-blocker Training Camp. Meaning that people aren't born with chi-blocking, they have to learn it and or train themselves to be able to chi-block.
More proof:
http://avatar.wikia.com/wiki/Chi_blocker_training_camp "The
chi blocker camp was a secret
Equalist facility used for instructing nonbenders in the art of
chi blocking that was hidden in a cellar underneath a bookstore in the
Dragon Flats borough. Following its discovery, it was invaded by
Councilman Tarrlok,
Korra, and the remainder of
Tarrlok's task force. Several people who had been participating in Equalist activities at the time were captured by the task force and arrested." Just because it says "non-benders" doesn't mean benders cant do it. What? So because you had an element your body says no when you try to master chi-blocking? I don't think so.