Going against the grain here from personal experience but I'm not sure it will give you a solution OP.
My brother was a straight A student, until A levels. He became distracted by the social life when he went from a single sex to mixed sixth form and his grades tanked.
There was never a question, in his mind, whether he was going to uni. It was happening. Like your son he had no set idea of what degree to take, and it became very clear that he just wanted to go "for the experience".
He really struggled, and his uni work was sort of fitted around his social life rather than the other way around. He refused part time work to give him some structure, only doing seasonal work in a supermarket in the holidays he bothered to come home for.
He was broke and failing. He finished the three years with a 2:2 while his peers were flying because they wanted to.
He then had the bright idea of staying to do a masters. Borrowed more money. His friends were going off and landing London jobs on good wages with their firsts and I think he didn't want to fail in the job market.
He got kicked out of the masters after a few months for failing to keep up. He walked away with basically a worthless degree and £60k of student loans.
I'm not saying a 2:2 is a worthless degree, but the field he chose was highly competitive and he had lofty ambitions of walking into a 50k a year job, without doing any work.
It sounds like this is what you're worried about happening, but tbh I'm not sure how you can stop it. If I could go back in time, I can't think of any way I could have persuaded DB not to go, or if he went, to actually put the work in/choose the right degree. He was blinkered that uni was as you say an entitlement but imo was just going so he could make new friends and party. An expensive lesson.