The sociology major has done a lot of work for you. If you think about the source of validity for an argument, ie, where the proof in the burden of proof comes from, religion's power comes from a divine source, not a cultural one. Traditionally the truth and power of divinity is meant to transcend cultural claims because divine power is of god, who created all things, etc, and is not beholden to any one culture. On the other hand, culture is a product of human interaction and is consequently manmade. Therefore by saying a divine claim is true because it is a cultural practice doesn't make sense.

In other words, Friend One says lighting candles works because god says it does. Friend Two says lighting candles works because people say it does.

So yeah, it's no problem to concede that lighting candles is a cultural practice. But that doesn't mean it gives enhanced intellect to college students. In fact you never made a normative (good or bad) judgement, but Friend Two changed the grounds of debate.

So on the question he changed the discussion into: this is where you have to be careful in arguing. Just because something is incorrect, doesn't mean that it is bad, per se. It's not too difficult to think of a situation where believing a factually wrong thing is useful or even good. It's easy to say Friend One is incorrect. The question is, why does that matter? From some perspective, we all act in absurd and ridiculous ways, eg - we're discussing minor religious quibbles on the internet while people we could tangibly help are starving to death around the world. This is especially important if you start to view religion like any other social institution, eg, democracy, capitalism, etc. They are mechanical systems but make up a part of people's cultural identity. So undermining a specific practice is more difficult because it is connected to a deeper belief I'm sure Friend One carries about himself and everyone that he loves, even though from your external perspective it is easy to question it. Basically your friend is weighing possibly improved test scores and acceptance from his family, versus the potential that he's wasting two buck on candles. If you want to change his opinion about this, he first needs to dissociate the practice with his core view of himself. And that, in essence, is why religion is so powerful - despite all the clear evidence against it.