The Kalam Cosmological Argument is one of the more nuanced arguments for the existence of god, and one that has been enjoying a revival in recent years. One of the big appeals that nuanced arguments have is that they tend to do a better job at masking the logical fallacies they contain; thereby making them appear more convincing. The argument is somewhat based on Aristotle’s cosmological argument, but was first used in its current format by Muslim scholars in the Middle Ages. It was later introduced to the Christian tradition through individuals like Thomas Aquinas.
Here is the argument:
1. Everything that has a beginning of its existence has a cause of its existence;
2. The universe has a beginning of its existence;
Therefore:
3. The universe has a cause of its existence.
As you can see, this isn’t, strictly speaking, a religious argument. It is, as its name indicates, a cosmological argument about the universe having a cause. This is one of the things that make this argument so nuanced – the fact that it has a non religious conclusion. Many religious apologists often point out that most of the opposition to the Kalam argument comes from confused atheists who don’t even understand it’s not an argument for the existence of god. This, however, is usually a ploy, since the only people who seem to use this argument are religious apologists who are actually trying to argue for the existence of god – they just do it in a creative two-part way. The easiest way not to fall for this ploy is to simply say that since the argument is not a religious one, it’s not relevant to a religious debate.
The way the argument gets tied up to religion is when two more steps are eventually added to the original form. This is either done directly or in an implied way, and usually looks something like this:
4. Therefore, the cause of the existence of the universe is god;
5. Therefore, god exists.

A good way to go about debating this argument is by taking it on one part at a time, so let’s begin with the firs part – the original form.
It might not be too obvious at first glance, but the idea that the universe has a cause because everything which begins to exist has a cause, is logically flawed. The easiest way to uncover the logical mistake here is to ask the simple question ‘How do you know?’ I recommend you ask this question as often as you can, since it’s one of the fastest ways of cutting to the problematic core of many religious arguments. When applied to the Kalam argument, there are, it turns out, only two ways this question gets answered – each leading to a different logical fallacy.
The first way is by appealing to observational evidence, and pointing out that everything we see had a beginning, and a cause for that beginning. One of the most famous proponents of this argument, the philosopher William Lane Craig, had said that this is “constantly confirmed in our experience, which provides atheists who are scientific naturalists with the strongest of motivations to accept it”. This might sound true enough (unless you’re into quantum physics, that is), but the problem here is that everything we can observe or experience is, by definition, observed and experienced within the framework of the known universe. Trying to explain the origin of a framework based on things that are contained within it, is a type of Composition fallacy. A Composition fallacy happens when you infer that something is true of the whole from the fact that it is true of a part of that whole, or even of all of its parts. Everything we know of might have a beginning, and a cause for that beginning, but we only know of things that are contained within the universe. To establish a characteristic for the framework of the universe itself, based on the characteristics of the things it contains is a logical mistake. In much the same way, we can establish that every single brick in a wall weighs three pounds, but to then say that the wall itself weighs three pounds, based solely on the fact that every one of its bricks weighs that much, is obviously wrong.
The second way this question is answered is by stating that even without observational evidence, by means of philosophical inference alone, it can be asserted that things – all things – do not simply begin to exist out of nothing. The above mentioned Dr. Craig puts it as something that is “rooted in the metaphysical intuition that something cannot come into being from nothing”. This, once again, might intuitively sound true enough to most people (unless you’re into quantum physics again), but there is another logical flaw here. To assert as a premise that every beginning has a distinct cause, is to assume a conclusion – which is a Question Begging fallacy. The fallacy of Begging The Question is a subtle type of Circular Argument, where the conclusion that you are attempting to prove is indirectly concealed within one or more of the initial premises. The main problem with the Kalam argument is that it attempts to make an arbitrary separation between Everything and The Universe. The term Universe is another way of referring to everything – or at least everything we currently know about. When we learn about something new we didn’t know existed before, we don’t say it’s a thing that’s outside of the universe, we expand our definition of what the universe is. In this sense, the terms Everything and Universe are interchangeable. So the way this plays out here is:

1. Everything that has a beginning of its existence has a cause of its existence;
2. The universe (i.e. Everything) has a beginning of its existence;
Therefore:
3. The universe (i.e. Everything) has a cause of its existence.

This, as you can see, is a simple case of repeating the premise as a conclusion; and a conclusion simply cannot logically supports itself by itself in this way. If this sounds a bit confusing, try, once again, to ask (or beg) the simple question, ‘How do you know?’ How do you know the universe has a cause for its beginning? If the answer is “Because everything that has a beginning, has a cause for its beginning”, then the premise is identical to the conclusion, isn’t it?
One of the reasons that many people become confused into accepting the Kalam argument is because they believe observational information and metaphysical intuitions mutually support each other here, rather than pile one logical fallacy on top of another. It’s also not uncommon to see people (like Craig) try to subsequently wiggle out of the Composition fallacy, only to wiggle right into the Question Begging fallacy, and vice versa. Craig himself has a celebrated YouTube video where he tries to refute the refutations of the Kalam argument. The video is full of these back-and-forth jumps from one fallacy to another, and also contains some miscategorizations of the kalam argument in order to evade a collision with a fallacy. In one miscategorization, Craig asserts that the Kalam argument doesn’t commit a Composition fallacy because it appeals to a scientifically inductive inference about the members of a single class, rather than to reasoning by composition. But this completely ignores the fact that parts of a whole are not in the same class of the whole itself.

Now let’s move on to the followup points to the Kalam argument – the points that make it a religious argument:
4. Therefore, the cause of the existence of the universe is god;
5. Therefore, god exists.
The problem here is that nothing has been presented in order to connect god to the universe’s beginning. It’s simply assumed that one leads to the other, which is a classic Non Sequitur fallacy. Again, all you need to do is ask ‘How do you know?’ How do you know the universe wasn’t caused by another cause, which was caused by another cause, which was caused by a deity? How do you know it wasn’t caused by something other than a deity? You don’t. You’re just leaping to the conclusion that a supernatural deity did it – asserting what must first be established, connected and then proven. And if the answer to this question takes the form of “What else could have caused it?” or “Can you prove it wasn’t god?”, then all you’re left with is an Argument From Ignorance, which is yet another logical fallacy.