how and why does ben use robert as a leader

Robert's mentality about The Wave is part of what frightens Laurie. She doesn't object to its principles, but rather to the 'creepy' conformity it inspires in her fellow students. Robert becomes popular in The Wave because he is the best at conforming. Strasser challenges the idea that the only way to achieve a strong community is for everyone to agree about everything.

"The whole idea of The Wave is that the people in it have to support it. If we’re really a community, we all have to agree.” Robert Billings