It's natural to have some doubt about entering a SA. I think most of us who've been through it have wondered, at various points, what the heck we were doing, why we were doing it, and what if we'd gone to that nice civilian school.
However, some candidates have serious doubts and ultimately feel they are being "forced" to attend a SA -- either b/c their family, school, friends, etc. are strongly encouraging them, b/c it's financially the best option, or a related reason. Many of those candidates end up starting at a SA and leaving very quickly.
To me, entering a SA is not unlike getting married. It's a huge commitment -- emotionally, legally, etc. Thus, it's natural to have a bit of angst. However, if the wedding day is approaching and you aren't sure this is what you want, better to back out before taking the vows -- even if you've booked the venue, sent out the invites, bought the dress, etc. Ultimately, it's a lot easier than having to go through the divorce.
Same is true about an SA -- better to decide before I-Day that it's not for you than to wait until August or October or some other time when the civilian college option is harder to implement. I suggest you try to talk with your son about the source(s) of his concerns -- is he worried about lack of freedom, military commitment, lack of "fun", limited majors, etc. He may want to talk with his BGO again. And he should visit the civilian schools.
The one reasons he should NOT -- absolutely NOT -- attend a SA is because "everyone is counting on him" to do it. Many candidates feel a certain momentum from family, teachers, classmates, friends, etc. that just pushes them along until one day they're at the SA and miserable. Resist that urge.