It is good that you have the insight to realize that it may be your understanding that is the problem and not the argument itself.
This is beside the point but I have noticed in speaking with atheists that they often simply assume that if they don’t understanding something, then the thing itself doesn’t make sense. So if religiomn doesn’t appeal to them, then they reject it (because of how it makes them feel emotionally) an then d begin to look for reasons and arguments which they can use to convince themselves that they have rejected it through superior logic and reasoning powers rather than because they didnt like the fact that God was smarter, wiser and more powerful than them.
I could sum up a large amount of modern atheism with the statement: “Christianity sounds silly to me/I don’t understand it, therefore there can’t be any truth in it”. They really are of the mindset that ideas which appeal to them are true and ideas which do not appeal to them are not true, because there could be no greater arbitrator of truth then their small minds. I know because I used to be an atheist and that was exactly how I thought. This can only happen in a society that has forgotten humility is a virtue, for atheism, which believes human beings are the most intelligent force in existence, is incredibly arrogant.
Anyway, back to the point. The argument is essentially that we desire for actual things, whether the desire goes fullfilled or not is irrelevant. But if you look at your desires, I think you will find that, especially the most powerful ones, are all geared toward things that actually exist. Have you ever someone who had a life crippling desire for a three eyed purple dragon for instance? Probably not. But I bet you ve met lots of people who had a crippling desire to find a marriage partner. Why is this? Why do we as human beings have a desire for a marriage partner but not for a three eyed purple dragon? Could it be because finding a mate is a real movement of human life whereas finding three eyed purple dragons is not?
Now, we all know human beings have a spiritual desire. A desire for peace and happiness which is permanent and transcends the immediate circumstances we find ourselves in. And we also know that nothing in the world of form is permanent. So the argument goes that the fact that we desire this, suggests that it actually exists. Why else would we have this INTENSE desire moving us to do all kinds of things which don’t even necessarily have a whole lot of practical/survival value if there wasn’t a way to fullfill this desire?
I also cannot say I understand what you mean by the outcomes on the other side of death. To die is one way to meet your maker but it certainly isn’t the only way. Jesus and the saints were able, to greater or lessor degrees, fullfill their desire for God even while still on earth. Remember Jesus said my peace I give you. That means not only that Jesus experienced peace while alive but also that he can give it to others, which means it is possible to have your desire for peace filled. Remember, Jesus said "Thy cup will runneth over, so he is not even talking about a small peaceful feeling, nay he is speaking about a major shift in conscious awareness. This shift is so radical that our Lord called it the “peace that passeth alll understanding”.
Anyway, I will finish with a quote from the famous Indian sage Sri Bhagavan Ramana Maharshi because he made this exact same argument:
“All beings desire happiness always, happiness without a tinge of sorrow. At the same time everybody loves himself best. The cause for love is only happiness. So, that happiness must lie in one. Further that happiness is daily experienced by everyone in sleep, when there is no mind. To attain that natural happiness one must know oneself. For that, Self-Enquiry, ‘Who am I?’ is the chief means.”
This might sound odd or even heretical to a Catholic, since the goal of our faith is to know God rather than to know ourselves but remember to know God also means to know oneself, for only through knowing God can one truly know themself/