You are right that saying that someone is 'playing God' is merely a rhetorical claim made by those who oppose the kind of actions that the person is doing are contemplating doing. Since, "given the impossibility of humans acting as gods," as you say, it is a way of saying that you should not do the action because it is inappropriate for a mere human to act in a way that is appropriate only for a god. Insofar as the claim has any force, and it does not have much, it is a warning about making fundamental changes without very carefully considering all of the consequences, long term as well as short term, of making these changes. Many actions have massive unintended consequences, especially those that involve changing how we deal with life and death matters.

There are different forms of utilitarianism, and they have different names. The view that we should aim at the best balance of happiness over unhappiness is often called hedonistic utilitarianism. The view that we should aim at the best balance of desires or preferences being satisfied over desires or preferences being unsatisfied is often called preference utilitarianism. They are both considered forms of utilitarianism because they claim that achieving the best balance of something, either happiness over unhappiness, or desires being satisfied over desires being unsatisfied, is the ultimate criterion for judging the moral rightness or wrongness of an action. Philosophers moved from hedonistic utilitarianism to preference utilitarianism because of the difficulty of coming up with an objective account of happiness, or even one that commanded anything close to universal assent. It was thought that desires or preferences being satisfied was a more objective criterion, and also one that was more tolerant...

There seems to be no more reason to heed the retrospective ideas, advice, and wisdom of a dying person than of that same person when he is not dying. If he is the sort of person who gave good advice previously, then what he says should be heeded; if he is the sort of person who did not give give good advice previously, then his advice shoud not be heeded. There is no reason to believe that dying makes anyone wiser than they were before.

There seems to be a set of virtues that every culture recognizes and appreciates, but they may not rank these virtues in the same way. For example, given the appropriate account, it is hard to conceive of a functioning culture that does not regard prudence, temperance, and courage as personal virtues, that is, as virtues that every member of that society would like to have. However, different people in a society and different cultures might rank these three virtues differently, some ranking prudence higher than courage and some the reverse. Similarly, there also seems to be a set of moral virtues that every culture recognizes and appreciates, but they may not rank these virtues in the same way. For example, given the appropriate account, it is hard to conceive of a functioning culture that does not regard truthfulness, dependability, fairness, and kindness as moral virtues, that is, as virtues that every member of that society would like the other members of the society to have. However, different...

If you mean by "hedonistic by nature" that human beings always act so as to secure the most pleasure for themselves, then your next remarks shows that you correctly do not think this is true. However, you seem to equate being hedonistic with doing what is in one's self-interest, and this is not true either. It is not always in one's self-interest to do what gives one the most pleasure. You also seem to take reason to be used solely to further one's self-interest, as if it were irrational to sacrifice one's own self-interest in order to save someone else from harm, but it is clearly rational to act in order to prevent a serious harm to someone else, even if it is not in your own self-interest. However, the main point of your question seems to involve the supposed conflict between reason and the passions. It is true that sometimes our emotions lead us to do something that will cause us harm when there is no compensating benefit for anyone. But, in general, our emotions do not cause us to act...

The morally right thing for the barman to do is to refuse to serve the clearly intoxicated senior member of the staff. He should also try to persuade the managers not to serve him. This answer assumes that it is true that the more senior member of the staff is clearly intoxicated. Given the truth of this assumption, the barman should point out to the managers that they are not acting in the best interest of the company that owns the bar. Most obvious, if the senior member of the staff has an accident, there will be serious problems for the bar and for anyone who served the alcohol to an intoxicated person. The barman could point out that his refusal should be taken as a confirmation of his good performance as a barman. By refusing to serve the intoxicated senior member of the staff, even under pressure, the managers can be sure that he will not get the bar into trouble by serving alcohol to clearly intoxicated drinkers. He can present all of this in prudential rather than moral terms, as moralizing...

The new thought does not invalidate the selflessness of your action, but it is morally unimportant whether your act was completely selfless or not. Most actions are done from mixed motives, and all that is morally significant with regard to how the action reflects on your character is whether you would have done it even if you were not to be rewarded for doing it. And since you initiated the action without thinking about being rewarded, later thoughts are of no moral significance. However, whether your act was morally good or right, or morally wrong or bad is not affected at all by whether your motives were selfless. Many immoral actions are done from selfless motives. Indeed, altruistic immorality probably results in far more harm than immoral actions done because of self-interest. Most of the people fighting in wars or performing terrorist acts are not doing so for self-interest, and may be acting from completely selfless motives.

If one means by virtues, character traits such as prudence, courage, kindness, and honesty, then, as Aristotle says, they are developed by education and training, although it must also be true that most people are born with the capability of developing the virtues. Hobbes points out that children learn more by example than by teaching, so that if we want to bring up our children to have the virtues we should exemplify them in our own conduct. However, some people mean by virtues, personality traits such as compassion and fearlessness. Personality traits probably are innate although they develop as the child grows and can be altered to some small degree. To talks about one's morality suggests that morality is a private matter rather than a public system that everyone one is supposed to follow. Although there can be some slight differences among people about what counts as moral, there is overwhelming agreement on most matters, e.g., that it is wrong to hurt someone simply because you don't like them....

It is not clear what it means to say that anything, especially means, are justified in themselves. It may be that the means do not need to be justified as they do not involve doing anything wrong. It is only actions that would be wrong if not justified that need to be justified. Many of the means that Machiavelli recommends do not involve doing anything wrong, so they do not need to be justified. But killing or slandering someone are the kinds of action that do need justification, and it is not a justification for doing such actions that they benefit oneself.

Some people value their pets more than other people, but one reason for holding that morality protects human beings more than other animals is that morality only governs the behavior of human beings, that is, in order to persuade all human beings to follow the moral rules prohibiting killing, causing pain, etc., all human beings must know that they have the protection of the moral rules. Neither elephants nor any other non-human animals that we know about have any criteria for valuing species. And morality is not related to species either; if there were another species that was required to abide by the moral rules, the members of that species would also be protected by the moral rules.