Duke Arsena ultimately did not insist on having John act according to his own plan.
He was very aware that the risks involved in his plan were indeed too great.
Duke Arsena simply wanted John to gather some information about the Dark Realm.
Once enough data was collected, John could make the final decision on his own.
"The risk of this plan is naturally very high. Moreover, the only person who can carry out this plan is you, as you are the strongest among us. If you decide not to take action, the rest of us certainly cannot force you to venture into the Dark Realm.
For now, you can take some time to gather information about the Dark Realm. After collecting sufficient information, make your own judgment. We will not disturb you in the short term.
