Eren possessed keen insight into how people thought in tense situations.
He particularly understood the concept of group mentality.
He knew that he would get targeted the moment other candidates realized he had been admitted into the test because of his preselection, thanks to the recommendation token given to him by Archpriest Jivem.
To the candidates who had proved their mettle by passing the initial rounds, Eren and others like him were nothing but outsiders. And outsiders would always get bullied by people who were in a particular situation or place for far longer than the newcomers.
Eren had experienced something similar in his academy days in LA. he had learned his lessons after experiencing life's realities personally. He didn't want to isolate himself and make the same mistake of becoming the target of all the bullies. Thus, he decided to become one with the bullies themselves by approaching them straightaway.