Wait so his crime was changing his mind.
Has anyone here not changed their mind at some point in their life?
Do we or do we not roast Janeway for changing her mind in some situations, such as not giving technology to the Kazon but giving it to the Hirogen? Tuvix can change his mind and not be seen as criminal but Janeway does it and she is? How many posters change their stance in a debate on this site and are criticized for it?
So yes, our online peers have already cast their vote that changing ones mind is a crime.
You're not seriously trying to argue that changing your mind and deciding to live is the same as Janeway saying "Ok, I'll give you some of our technology" are you?
It doesn't matter how the being Tuvix came to be, he was a unique lifeform. Janeway's ruling was basically to murder him. He commited no crime to speak off, he had no saying in how he was created. Last I chceked there was only one offense that warrented the death sentance in the Federation, visiting Talos IV.
We generally don't punish people for things beyond their control.