It is even more arrogant to assume that all human beings have authority over what is right or wrong. Consider that this belief is how tyrants were born.
Please do not confuse belief with truth. Beliefs can be irrational, truths must always be rational.
It is undeniable that the government of a country has more power over the laws. But legalizing slavery (for example) still does not make it "right" or "good". It presupposes that some people are superior to others, which is debatable.
"Who determines morality" is an invalid question simply because it presupposes that some human being gets to decide what is right or wrong. Anything a subject decides may be subjective, i.e. it may depend on the mental state of the subject. The correct question is "What determines morality", and the only way to determine objective truth is to determine the nature of the objects in question.
Who can deny that electrons exist? These objects exist independently of what we think, hence their existence is objective.
"What makes certain actions inherently wrong" is the central question in Ethical philosophy. I do not have the required knowledge to answer this question yet. At this moment I am simply saying that morality cannot be subjective if the notion of morality has to be maintained. To say something is moral is to say that something else is immoral, and morality has to be in the object for this relation to be maintained consistently.
What you mean is that virtually everyone creates their own set of principles to deal with the world. That doesn't make the principles right or wrong though. Furthermore, the more subjective the set of principles become (the more changes you make to your principles), the less moral it is. Principles that allow oneself to achieve their goals and motives should not be confused with morals.