You are correct. I caution against it in my classes. One of the real dangers is that couples can be very protective of each other and often will lie after the fact.
I would probably intervene if I thought a life was in danger, so never is a bit too strong for me.
Way too many times if it is a couple no matter how bad it gets from the other partner the other one sticks up for them.
Unless one personally knows what is going on I would not get involved. I would not intervene with out the power of the uniform to back me up.
With that one has the option of throwing both of them in jail if needed it has been done many times.
again you may not know the reasons behind it, they may be defending themselves too.