If I remember correctly there are 3 things you can't do to save a life: illicit relations, take a life and idolatry.
Meaning even that if you do find yourself in a situation where cheating on your wife would actually save a life then it will still be forbidden
no it is not, it is called that only by those who does not follow (and which these same rules does not make a difference in their lives) and for some reason feel entitled to be offended for others
I once heard that because of this one should make an hydraulic elevator, so the passenger weight would not affect the energy used, not sure if this holds true or if it is even practical