Ever since the incident with the Sludge Villain in middle school, where Bakugo was nearly taken over by a slime quirk, he has been deeply averse to being restrained in any manner, and the kidnapping only exacerbated this. He is terrified that something like it will happen again, where his weakness could lead to someone he cared about being hurt. The idea that he was completely helpless to stand up to them stings in his mind, and the last thing he wants to do is admit any of this to anyone.