At least, you can try to use all the rational arguments in the world and still not be able to make a decisive case. The name “Jesus” in the post title could be Jehovah, Allah, Brahma, Zeus, Odin, Ra or any other supernatural deity that people have chosen to worship and to believe represent the ultimate explanation of the Universe.
So why try? Let them believe that Jesus loves them and will greet them in heaven and don’t even make the logical case against it. Again, it’s not that you can’t make a pretty good case – in at least outlining why such a belief is extremely unlikely to be representative of any sort of reality. You can make the case, but you can’t – as we in the atheistic, rational, skeptical, scientific community well know – demonstrate it with empirical evidence. We don’t have evidence that there is no god (and we never will. By the very nature of the question, we can’t prove a negative). We can prove that a proposition is so, but not that which is not so.
So is it being advocated that we just shrug and accept the boatloads of non-sense that float into our lives every day, everywhere in the world? It would be defeatist to make such an argument and things are not hopeless. Things are bad, but they aren’t hopeless. What we need to do is adjust tactics. By changing tactics, I’m not talking about using a different weapon. I’m not saying we should use humor instead of reason (although, as an occasional weaponry adjustment, that can be good). But “tactics”, in this case, means looking at the larger battle field of rationality and seeing where it is that we can make the biggest impact. It’s not the corner of the arena where sits the throne of god.
While there is no real need to worry about the supernatural beliefs of others, there is a lot to be concerned about any time and any where that those supernatural beliefs stray into the parts of the field that contain reality and nature. That’s where it gets interesting – because it is indeed possible to clearly demonstrate that people are wrong in those areas. They will not accept the evidence immediately. In some cases, for some of them, they may never accept it. But when the vast majority of people accept a given proposition as being a truthful and accurate representation of reality, then those on the extremities of the argument become so marginalized as to be a non-factor in the discussion.
It is a historical fact that a mere 550 years ago, no one on this planet had heard of Copernicus and if anyone thought the planets (including ours) moved in orbit around the Sun, they weren’t saying it out loud. Indeed, they would have known that doing so would mean a certain death warrant from the Christians (The Catholic Church, specifically, which was the Christian Church at that time). It would have meant their execution, because the Christians (along with believing that Jesus was up in heaven waiting for them) thought that the Earth was the center of the Universe. So a factual claim from faith came in to direct collision with science when Copernicus and then Galileo demonstrated otherwise.
We might like to believe that once the scientific knowledge was out there, the Church quietly accepted it and within a short time the entire world had a new view of the cosmos. Oh, that reason could work so quickly! True believers disputed the facts of science for hundreds of years until today it seems almost quaint that many folks once denied the fact. But deny it they did, and for a very, very long time. Can we draw any modern day corollaries? It seems like there are quite a few that continually frustrate us. It appears that, no matter how strong the evidence is, we can never get it into some peoples’ heads. But we can! That’s the nature of evidence. It’s on our side today and it will be on our side in a thousand years. The Earth, 550 years later, has not slipped back into its geocentric position. Over enough time, and with ever increasing, never decreasing evidence, virtually every person on the planet today accepts the truth.
Most of the repugnant factual claims associated with major religions (specifically, but not exclusively Christianity, Islam and Judaism) have already been firmly shown by science to be “other than believed”. Our job is to keep battering away at the gates of ignorance. We may have to say some things 10’s of thousands of times and acquire more and more evidence. But we have the facts on our side. Theists can still run to refuge in their little castles in the sky, which can not be disproved, but those will become lonelier places for those who continue to seek comfort there.
Resist the obvious temptation to debate the generality of god, redemption, salvation, heaven and hell. This is where most arguments with theists will begin, and, while undeniably silly, are not subject to your knowledge, rationality, reason, logic or science. Instead, immediately turn the discussion to the factual claims made by whatever religion is being debated. Some of these claims (certainly not all) will include:
Evil acts are exclusively the result sin (separation from the holy spirit) in a context of free-will as given to us by god.
The power of prayer has an effect on natural events.
The world was created pretty much as is, in 6 days, between six and ten thousand years ago.
Evolution can not be a fact because god created all of the life on earth, exactly like you see it.
An abortion in the first months of pregnancy is the same as killing an adult human being.
Homosexuality is a sin, a perversion and an abomination in the eyes of god.
Homosexuality is unnatural and is a choice made in a context of free-will as allowed by god.
Update 2/15 - For an explanation of the change, please see the Exterminator's comment.