To speculate on Michael's course of action with Tom we may have to review his history with other business and personal relationships. Did Michael kill (or have killed) anyone who was NOT in direct conflict with him? McCluskey and Sollozzo - tried to kill his father. Tessio - betrayed the family. Carlo - set up his brother. Barzini, Tattaglia - conspired to kill Vito and him. Cuneo and Stracci - hmmmm? guilty by association with Barzini and Tattaglia?? This one could be a pre-cautionary elimination. Fabrizio - killed his wife; intended to kill him. Fredo - betrayal. Hyman Roth - tried to kill him. Geary's prostitute - to neutralize Geary (not nice). Tom Hagen....maybe a precautionary like Cuneo and Stracci, but ???? He very well could order it. Paranoia was becoming a dominant trait.