It’s less directed at a single character, but I think the whole synth personhood argument seems like it would be a good thread for development.
We saw from Dr Pulaski’s reaction that even the most understanding and well-meaning members of Starfleet can still have reservations about whether a sapient machine is a person, or just a machine, even if they come around once they get to know them.
We also know from Maddox, the crew of the Sutherland, and the Voyager that some less well-meaning members of Starfleet see them as walking computers, and little more, until they are forced to see reason (whether they come around at that point is unclear, considering the Lal incident).
The Voyager’s crew even went as far as to try and solve the sapient EMH’s issues by treating him like a faulty computer/software, whether by fiddling around with his code, or factory resetting him when things went wrong.
We also know later on that while Data has his rights and personhood relatively firmly established, that ruling applies to him only, and not to any other inorganics. The Voyager’s EMH had to have an entire legal battle to determine whether he would own the rights to a book that he had written, whereas that would not be in the question, had the book been written by a biological humanoid.
There’s also a subtle plot where the Federation can and will use them as effective slaves, even if sapience is unclear. The other Mark I EMHs are used for dilithium mining, and Maddox’s reverse-engineered schematics of Data were stripped down, tweaked, and used to create a non-sapient synth workforce, despite his protests.