ethics and abuse

I was wondering today about abuse, and basically how that is basically treating a living entity like an object; a means to fulfil whatever desire one has with no respect to the cost and consequences that others have to pay - how abuse is a complete and utter lack of empathy towards the victim, caused by being entirely consumed by what one wants for themselves.

that was a scary thought, because I can see that attitude to be so very pervasive - I knew of a kindest nurse who would take care of really sick bed-ridden patients but asked me why I was vegetarian when "God created animals to eaten by us", the argument I have heard made at other times by other people I respect.

basically, I am asking, what is the basis of ethics? and how can we answer that without knowing what is the basis of desire? and isn't that like asking the flip question, if God* - the most ethical and powerful entity - is good, how can we have desires that can hurt others? if God is good why is there evil in the world? or if we are purely selfish people how is there any good?

but on another level, I am asking, how must I interact with the world? this world brings me joy, and I am attracted to the people who make me happier; what is worse, I avoid people who give me grief! how must I live that I don't treat people as means to an end?

UPDATE: Relationships are giving and taking of joy due to the presence and actions of another being; but when these become one-sided, that is when relationships become abusive.

*interestingly in Vedanta I have only heard God being Sat Chit Anand OR Satyam Shivam Sundaram Truth-Pure Knowledge-Pure Happiness; OR Truth-Auspiciousness-Beauty; and then, if you are interested, here is a rather interesting article by Dr. Martin Luther King Jr. on "Religion's Answer to the Problem of Evil" where he says,

"In sharp contrast with the view which justifies all evil as good is the view that evil is unreal. It is "maya" or illusion; it is "error of mortal mind." This view has its strongest proponents in Christian Scientists and Hindus. Objections to this are obvious, ... As Dr. Whole so congently states in a criticism of this theory, "To say that all suffering is a delusion of man's mind would be to make the existence of the mind the worst of evils; there is not much to choose between pain that is objectively real and mind which necessarily imagines the pain that tortures it." 

and that is what Hindus says, this mind is a problem, purify it and get rid of it - for right now we don't recognise anything beyond this mind.