I dont see anything wrong with it, as long as he is honest about it, and as long as he does not claim to believe nor profess to be a christian if he is asked about his faith or lack of it.
On the other hand, if he “pretends” to be a christian when asked by girls or others, then he is a two-faced hypocrite liar and a fraud, and it is definitely wrong. Neither should a non-christian take communion nor engage in any leadership roles at a church(e.g teach sunday school) .
Just wanted to be the first to say “purpling” is one ace wonderful expression 
Look on the bright side. Maybe he’ll be a positive influence and draw the girls away from the flock.
Pun intentional?
I met my current gf at a church thing… im not sure what it exactly was, maybe a youth group of a sort. Well, one of my friends that attended the church started it up, and everyone that attended was in high school. Well, to cut to the poin, me and my gf arent very religious. Me, im almost atheist (if that can happen). I openly shared my anti-religious beliefs and often challenged the scripture they quoted me. I dont think i offended anyone, but i thin that sort of thing they like because it makes them develope better ideas about how to relate to more people.
RElating more back to the OP ?, i think that it isnt a bad idea to go to church to meet/get/score/whatever girls, but the downside of that is that most religious people (at least in my experience) tend to be very closed-minded on a variety of issues. This makes discussing even hypothetical topics very excruciating. Their views often can be bigoted.
Look on the bright side, most kids have to be dragged to church. Yours go willingly.
Building on what Bump said about community, I would say it’s not right to go to church to look for a mate. Not from the moral perspective, but from the perspective that communities increase not when its members intermarry but when its members marry from outside. So if the son plans to join to meet women, he isn’t doing the church a favor.
Girls who go to church have very high moral character – none of them has ever agreed to go out with me. I have gone to church with the hope of meeting people, especially female people, and had rotten luck. YMMV.
I did, however, end up as Chairman of the Education Committee. But that’s another story.
I’ve never gone to church with the goal of meeting women, but I DID meet my wife at church.
So, it can happen.
At least at church you know what religion they are…
I don’t think this was mentioned yet, but here on Long Island (NY, where all the fun is), Catholic Mass is a pretty darn crappy place to meet single women (take it from a single Catholic guy who has attended Mass fairly regularly for decades) - not sure how widespread a region this holds true in.
There is a phemonon around here where (in general) single women stop attending Mass sometime around age 16 or so, and reappear in their late 20s/30s with their husband and kid(s). There were alternatives in Catholic Youth Groups, dances, nights outs, retreats, outdoor events (former LI YAMers, remember the Fall Young Adult Conference!), but they seem to have fallen by the wayside for some reason (Personally, I think it’s due to a lack of single women in their 20/30s around here - single men like me, we’re a dime a dozen, but that’s another story…)