Stratt was absolutely right to conscript Grace for the mission and any executive officer would do the same in that kind of emergency.
Stratt is completely out of options. DuBois and the backup were dead. Dead to an error that Grace would have caught and DuBois didn't, by the way.
There are no qualified volunteers ready to take the mission now. The time taken to train a new specialist and calculate a new launch window would be measured in 7 digit human casualties. There was no time, and exactly 1 human left in the world with the expertise to pull this thing off.
Stratt was trying to save her species and did not have the luxury of coddling Dr. Grace's qualms. The emergency she was facing was easily of a level where individual rights go out the window. If Grace didn't man up on his own, she had to either conscript him or doom perhaps millions of humans. She worked with him as long as she dared, hoping his better nature would win out, and then when it didn't, she made the move that her role demanded.
Grace was trying to doom his entire species due to his own self doubt. That was not happening on Stratt's watch no matter how much she liked the man..
The astrophage response had Dr. Grace's fingerprints all over it, he was by far the best qualified man for the mission, and he was young and healthy enough to risk the voyage. At the end of the day his species' survival depended on Dr. Grace being on that spacecraft, so Stratt made sure that he was there.
The people whining about his freedom got sucked in by the book's conceit of telling the story from Grace's own perspective. Ordering a man to his death to save the group is something executive officers just have to do sometimes if if the occasion rises to a certain level of seriousness. That's exactly what Stratt did, and it's a perogative of leaders in any crisis of this magnitude.
Was it a violation of Grace's rights? Probably, but his integration into Project Hail Mary came with a duty to see the mission through and save humanity. He was part of Stratt's command chain, so when the sequence of events made him the only viable option, she was likely well within her authority to sacrifice him.
I do like the movie making it extra clear that Stratt didn't enjoy any part of the process of sacrificing Grace. Grace was a friend, and a key figure in Project Hail Mary. If she had a viable alternative she'd never have done it. But she did not.