Here is an interesting question from the studio audience.
[D]oes [the fact that the malleability of desires change] mean that what was wrong (right) in the past can become right (wrong) in the present due to the maleability of desires?
The answer is, Yes. What is right or wrong can change over time.
Now, actually, we have to look at different levels of morality here. At one level, what is wrong (right) does not change. It is always the case that the right act is the act that a person with good desires would have performed. What is wrong is still what a person with good desires would not have done. At this level, morality is constant across time, and across situation.
However, what a person with good desire would do depends on the circumstances. A person with good desires would tell the truth, generally. However, she might not tell the truth to the Nazi soldiers who are looking for the Jews that used to live in town – Jews that she is hiding in her root cellar.
More to the point, however, what counts as a good desire can change over time.
In a society with scarcely any water, and which is particularly dry or particularly cold, it may be worthwhile to promote an aversion to bathing or even to getting wet. However, if this same community should suffer a change in climate, where rains become pleantiful and temperatures become warmer, they may discover that it is now best to promote a desire for bathing and an aversion to having gone more than a day without a shower or bath.
One of the principles of morality is that 'ought' implies 'can'. It makes no sense to say that agents 'ought' to have a particular desire that they cannot have, or ought not to have a desire they are compelled to have. However, as scientific research increases the range of possibilities, it increases the range of options that are available for promoting desires that tend to fulfill other desires, and to inhibit desires that tend to thwart other desires.
One thing that is important to note is that the fact that a fact changes over time does not prevent it from being objective. For example, another thing that has changed over time is my age. It has changed at approximately the rate of one year per year. Yet, at any particular time, there is an objective right answer to the question, "How old are you?"
Similarly, at one time I was shorter than my mother. For a brief period of time I was the same height as her. Now, I am taller. However, the fact that this relationship has changed over the years does not in any way prevent claims about our relative height from reflecting objective fact.
Also, whether something was right or wrong at a specific time does not depend in any way on what the culture believed or what their 'values' were at the time. People in the Middle Ages might have thought it wrong to bathe. However, the fact that bathing helps to prevent the spread of (desire-thwarting) disease means that they were wrong to believe this. They should have been promoting a desire to bathe, not an aversion to it. Morality is neither individually nor culturally subjective. It is, instead, relationally objective.