I think the most important person in your committee for you for the defense of the thesis is your supervisor. If your relationship with him/her is not good, then probably you should be afraid. It doesn't mean other committee members aren't important, but usually if a member tries to corner a student in the defense, his/her supervisor will defend them, in which case the member cannot continue, at least without intellectual confrontation with the supervisor, because afterall a PhD studemt's work is his/her work, too, in a sense.

I remembered a story and I would like to share it: I know a PhD student who wasn't communicating with his supervisor, and he (the student) pushed him (the supervisor) for the proposal, and the supervisor agreed, but he (the supervisor) failed him (the student). The funny thing is that, usually supervisors defend their students, but what happened with this student is that all committee members were nice to him, except his supervisor!! I'm not sure what happenedn next, but I think according to the rules, anyone fails the proposal will be kicked out of the program.

However, a professor in or out of the committee can fail you in his/her course. In PhD failing a course is very serious. Normally, two Fs and you will be kicked out of the program. So, I would say make sure first that he/she won't fail you in the course.

In the end, thinking long-term is better than short-term. If working outside the university is conflicting with your study, try to have a TA position, for example.

Good luck