The whole question reads thus
If you believe there is no God, why not do whatever you want to whenever you want to? There really is no consequence if there is no judgment by God. If there was no God, I would use mind altering drugs, have as much sex as I wanted, hurt people who angered me, or whatever. Sure, people wouldn’t like me, but that is a temporary condition solved by death. As the Apostle Paul said, “If the dead are not raised, let’s eat and drink, for tomorrow we die.” (1 Corinthians 15:32) As an atheist, do you live this way? If not, why not?
This is a very loaded question and is often asked of atheists directly or in many variants. To deal with this questions, I would first want to take a detour to briefly demonstrate why claiming our doing good as being dependent on the existence or say so of a god is not tenable. To do this, I will present the Euthyphro dilemma that appears in the writings of the divine Plato, as Nietzsche calls him, where he presents a question Socrates asks Euthyphro and is presented thus:
Is the pious (τὸὅσιον) loved by the gods because it is pious, or is it pious because it is loved by the gods?
which is loosely rephrased to read
do gods command a thing because it is good, or it is good because a god commands it?
If in the first instance you answer yes, then it can easily be said that an action being morally good has nothing to do with gods say so. On the other hand, if your answer to the second question is a yes, then anything a god commands is moral. There are theists who have argued that this is a false dilemma that god is by nature good and as a result he cannot command an immoral act. The argument that god is naturally good presents a problem if the theist also argues that her god creates everything, for then the question to ask is why would an infinitely good god create evil. For a moment, granting there is a god, such an entity is made known to us through scripture, where we find situations where he has commanded murder [Exodus 11] or been complacent in the commission of murder [Judges 11:31-40] though this depends on whether you consider human sacrifice/murder moral or immoral [taking Christianity as an example]. It is evident from the above examples that to rely on the say so of a god as a guide for morality would be a disastrous exercise without a solution in sight, especially given the fact, that whenever god has spoken, he has not addressed himself to everyone in a language they all understand but has always chosen to do his speaking through proxies.
Having thus dispensed with whether gods have a say so in our morals, we can then look at the questions presented each at a time and see what we can say in response.
The first question asks
why if there is no god, should I do good?
As must be obvious to anyone who has considered this matter, how we act is directly linked to our living in societies with other sentient beings. That this is the case is evidenced by the fact that almost everyone would be bothered by the reproach he would receive from his fellow-men if his conduct was wanting than what a god would think of the matter. We daily observe, men being so concerned about how their neighbours would perceive them if they acted in a certain way than what the heavens thought of the matter and is further supported by the fact that many crimes are committed in private, where we would expect gods to be on watch, even by god believers, than in the public glare. It is important, therefore, to note that the threat of a future punishment in the hereafter can not act as a deterrent for committing crimes in the present life. Many crimes would be committed if the offender was certain he would not be caught, even if he thought heaven was watching.
To say there is no consequence for our actions unless a god exists is to ignore the fact men have lost their honour among fellow citizens, have been incarcerated, or in some cases killed by the state for being a disturber of peace! The threat of punishment in heaven has not made societies better. On the contrary, men have been most unhappy where the belief in god and of nether worlds has been rampant. In truth, where leaders have thought themselves answerable to god alone, men have been most unhappy. The rulers have been cruel, inconsiderate, and, believing themselves answerable to god alone and having priests as their cohorts, have waited for the last possible moment, when they can no longer inflict any more evil, to ask heavens for its forgiveness. It must be evident that men are concerned with how their fellow men will view them than with what heaven thinks.
The last part of the question implies that whoever is asking it, is stopped in his tracks only because he fears a god who would judge him after he is dead. Such a person is not fit to live in a society of men, where we owe our fellows obligations such as not abusing their rights. Because I am organised in a certain way, that is, valuing peace, honour among my peers and those around me and fear of pain, among others, I do not go around offending my neighbors. In fact, this is hardly a choice, and to claim that I chose not to offend my neighbors, I think, would require to be supported with evidence. Whereas I know that my death will be the end for me, I don’t know when it will come calling and wouldn’t imagine living in a society for a minute longer where I am ostracized! No one cares for a miserable existence among his fellow men. Those who live their lives trampling on others rights have lost the capacity to empathize. They, in my view, no longer view the other as being like them, but see them as quite distinct and separate, in a word, as being less human.
To include sex in the list of things that this person doesn’t do for fear of gods is to treat sex as an evil, a wrong that should be avoided. If sex is a natural desire for living creatures, there is, indeed,no way that having sex then becomes good or evil. The question one would ask, is, why, if this person believes he was created by god, did god find it prudent to have sex as the most profitable way for the propagation of species and why did he make this desire so strong?
In conclusion, I do not live as Paul suggested we should live, not that I don’t enjoy my beer, I do, and not because I fear a god, but because the reproach of my fellow men in this life and how they see me is more important to me than the fear of a supposed heaven or hell. Two, as I have written elsewhere, I do believe that our training, environment and temperament determine how we act. These things rule out whether I actively choose to or not to do some specific act. In short, I have no choice but to act as I have, whether everyone agrees with this conclusion is open to debate.