If he gets involved, then you will need to intervene.

[Bedivere may have been an average servant, but even 'average' was dangerous to humans. If something happened to him and he lost control of himself, he would need Dazai to fix him up.]

I'm sorry to put that on you, Master. But I'm a straightforward fighter, I have no way to deal with an ability like his. Other than by knocking him out.