As a human being you always have rights, and to me the biggest right of a sub (or slave) is the right of consent. You choose to submit yourself to your dom, and to me a good dom is honored by the gift of your submission, and would not want to threaten that by doing something that might make you question whether you want to do this anymore. Of course there are hard limits. Everyone has hard limits. You need to be able to talk to your Master about what they are and ask them if they will respect that. They should be honest with you whether they will respect it. And then based on their answer, you need to decide if this relationship is right for you.

I think it all depends on your general happiness. If you're happy serving your Master and are happy being their slave, then suffering through things to please them is fine (and can make you feel good when you know you've succeeded in pleasing them). But if you find yourself generally miserable because most of the time you're doing things you don't want, then maybe you have a mismatch and need to find a different Master.

For myself, if I find a sub truly resisting and not wanting something, I'm interested as to why they are refusing. Do they just feel embarrassed? Then of course I will make them do it. Do they truly feel frightened for their safety? Then let's find a safer way to accomplish it. Does the activity cause them pain "bad" pain as opposed to "good" pain? Then I would never push it. Is there something that I don't know? Then my sub is lying to me and we have trust issues, and that needs to be immediately resolved (I am HUGE on my subs not keeping secrets; they may not have thoughts or feelings I don't know about).