Reasonable to exclude a specific professor from a thesis defense for personal reasons? When I started my Master's program, my supervisor was Professor X. However, I had to leave their group after a few months, partly because we didn't get along, but also because the research topic wasn't a good fit.
Presently, my supervisor is Professor Y (who is awesome, and with whom I performed research work that really interested me). Now, I am getting ready to defend my thesis and need to select professors for the defense committee.
It so happens that my current thesis research deals tangentially with Professor X's research focus from about 5 years ago (and by the way, there aren't many professors whose research directly relates to my thesis). Under normal circumstances, Professor X would have been a decent choice for my defense committee.
Here is where I need a gut-check: I personally do not want Professor X on my defense committee. It is unlikely that they would try to sabotage my defense, but I have always found it distressing to be in Professor X's presence. Yes, I could grin and bear it, but I would simply rather not do that. Is it reasonable to request that Professor X be excluded?
This is something to talk over with your advisor. It is a reasonable request, but it might not be possible to go along with it. But if your advisor knows the whole story they can advise you on how to proceed, or even, if necessary, assure that the other person isn't included.
But, assuming that your advisor is present at the defense, perhaps one of the examiners, then they can intervene if there is anything improper going on.
If the advisor isn't present, it is a bigger problem, and you need to work harder to achieve the other person's attendance. Sadly, there may not be any options, given the field and the available people.
But, you need an advocate in setting it up and preferably at the defense as well.