I don't think Arum is scared of putting Pacquiao in with Mayweather. Win or lose Pacquiao only has a couple of fights left regardless and the minimal financial impact of him losing to Floyd would be far outweighed by the amount of money the super-fight would make.

I just think that he really dislikes Floyd because of their past, doesn't want to work with him, and doesn't want to be part of making him money. It's sad and an example of the factionalism which is helping to marginalize boxing.