1) He wants to keep an "open mind" toward a known cult leader/cult system.
2) He believes there are always "two sides to every story" (See point 1). The cult leader/system that wants to attract apologists also always insists that there are "two sides to every story".
3) He meets the cult leaders and finds that they are friendly and "cool". They seem nothing like the villains they are portrayed to be. They give him a strictly-controlled "guided tour" filled with flowers, clean houses, strange but good food, and the always-smiling faces.
4) He strikes up a friendship with the cult leaders. When confronted with negative facts about the cult, he brings up this friendship over and over. He's not hanging out with the cult leaders to either endorse or judge them. They are just his "friends". He says this over and over.
5) Former cult members/victims try to contact him to tell him that he is being used and that he has been manipulated by the cult leaders. He states emphatically that he is a friend of the cult leaders (See point 4), implicitly rejecting the harrowing testimonies of any who are not the friends of his new "friends". The more he is pressed to research the dark side of the cult that he has glossed over, the more he "doubles down".
6) His indoctrination now complete, he now advances to active apologism. "The cult isn't so bad. You guys are too negative. Look at all the positive stuff they're doing."