The reason Kenta attend hope's peak is to stop junko plans
kenta is not inherently evil ,he is just as selfish
He is overconfident that he survive the killing game
So he attends to prove himself in the killing game
So he makes some plans to use junko to achieve his dream
his organisation is more secretive and not powerful than togami
Even celestia made some trouble with his organisation
And Kenta is not a normal person
he is a intelligent progidy remember, he is just like a mafia man
Listen kenta has a shitty life
no one cared for him,no one stood up for him ,when he needed their,so he got the idea ,that all people are bad,so he don't regret betraying them,it's not due to just parents
He is a bit paranoid about trusting people
Junko erases his memory just like she did kirgirl,since he can over throw her plans