"If these concepts are merely social constructions, or human opinions, whose opinion does one trust in determining what is good or bad, right or wrong? "
Good question! What is a social constrict? It is something that a person or a group of people make up in order to say that this is "good" and this is "bad". But then you'd have to ask yourself whether that would be true in ever situation and in every culture.
Think about all of the different cultures in the world and how they have different beliefs of what is right and what is wrong. Who's to say which one of them is right? Are they all right? Are they all wrong?
What it comes down to is that You are the only one to say what is right and wrong, good or bad in your life. The only indicator that you would need is the one that is built-in to your whole being. If it feels good, it's right; if it feels bad, it's wrong.
Society and Religion make all of these rules up about what we can and cannot do. Ask yourself, do you follow every single one of them? I bet the answer is No. Why do you think that is?