. . .blah. . .bla-blah blah. . .
Tuvix wasn't an entity that possessed them. Tuvix was a sentient being created from them.
He did nothing to cause it; he was the result.
If I were a captain in that situation (and thank the gods I'm not, having no military experience), Tuvix's guilt or innocence would be irrelevant. He's preventing me from getting my crewmen back, and I will do anything necessary to have them returned. It's a hostage situation.