Haruka believes in efficient, effective strategies that make use of the strongest thing around. Gigas has a technological and, especially, vehicular advantage over Union. But if that were taken from them, a group could infiltrate the Gigan army and get close enough to a Gigas to try and 1) determine how they're being controlled 2) disrupt said control.

tl;dr

WHO WANTS TO STEAL A GODSDAMN TANK HELICOPTER.