You don't have to and you're not supposed to follow illegal orders.
HoloGeordi just shuffled off to his own death because he could see that it was his duty to say the ship and the other thousand people on board Enterprise.
But he could have just as easily said "Go fuck yourself."
Well, not just as easily, his sacrifice meant that a thousand people would live and that's hard to ignore.
Tuvix's sacrifice meant nothing.
The ship wasn't in danger, he could do both Neelix and Tuvok's jobs.
And he'd win over Kes eventually with persistence.
Were Neelix and Tuvok struggling to get out, or were they happy inside him?
Tuvix claimed that they were happy and his parents.
Seems like a slam dunk.
On the case of Sim.
That guy had a seven DAY life cycle.
He refused to help Trip because he believed that if he missed the window where his parts were ripe for Trip's ailing body, that in the remaining 2 days left to him, that magically Phlox could give him another 40 years.
I forget. Did Phlox find a way to give Sim another 40 years and still cut him up for parts, or did the Doctor run out of time?