An argument is only ever as strong as it’s weakest premise. I assume we all agree on that. The weakness of one premise will pass down the chain of reasoning and no conclusion based on it can be stronger than that weakest point.
I’d like to look at what seems to be a fairly popular argument amongst apologists with that in mind. That argument is the First Cause argument. There are various forms of this argument of varying degrees of sophistication. The one I am going to use is one which is not particularly sophisticated, but it is very common, so worth debunking.
The First Cause Apologist argues thus:
1. If the universe began to exist it must have been caused.
2. The only possible cause of the universe would be God.
3. The universe began to exist.
4. Therefore the universe was caused
5. Therefore God caused the universe.
6. Therefore God exists.
This is not self-evidently true, so must count as a weak premise. There is no good reason to believe that the universe was caused. Cause and effect operate within the universe but we cannot assume that they exist independently of it so as to apply to the universe itself. An analogy would be a game of Monopoly. Within the game we move according to the throw of the dice, or the instructions on the board itself, or cards. But in order to start playing the game, we did not have to throw any number on the dice or read from a card. The way we play within the game is in no way related to the fact of the game being played.
Another weak premise, if we are to understand by “God” the Judeo-Christian deity. If the universe was caused, it might have been caused by some impersonal force. Or by an imperfect being. Or by a being which has since ceased to exist. Or by a number of beings.
This is often considered by apologists to be their strongest point but it is as weak as all the preceding ones. There is no scientific agreement as to whether the universe has always existed or not. There is scientific consensus that the universe as we know it came into existence about 13.8 billion years ago but that does not mean that scientists all agree that everything which now exists came into existence at that point. This point was well made by Sean Carroll in his debate with William Lane Craig, which can be found here
For those who want the edited high lights, this does the job very well
*I have assumed for the purpose of this post that God is not a logically incoherent concept.