So yah if my mother in law is demanding i would do my best to understand her point of view and adjust however if she is just demanding me to do something thats against my ethics, morals i will sit down with her and let her know.
No sane person can ask you to do wrong but if its just different customs then i had try and strike a balance. See even parents at times have different views than you but that doesnt make you leave them or dislike them.
NO desi MIL would sit down and have a heart to heart chit chat with her DIL so they can work things out.
It's great that you have such open mind and would like to keep things in balance but that would only happen in Utopia (I believe someone has already said that).
And yeah it would be THE SANE PEOPLE who would say and do stuff that would make you go....are they for real? Why are they actin so insane.
However not all inlaws are evil. There are some real messed up dils out there as well. You do your part by doing everything right and hope for others to do theirs. But if you think everything is going to be fine and dandy all the time then unfortunately that's just being in denial.