Looking at it from your son's point of view, if he really hates uni, the best thing he can do is leave it and go in search of something he does want to do.
I went to uni for a year, really didn't get on with the course, and failed my first year. Uni invited me to repeat the year, which I considered, but I got a temp job in the summer holidays which turned permanent, so I declined and dropped out of uni.
The following year, because I had a job I managed to buy a (cheap) flat (I was 20 at the time), which I then sold and bought a house which I now rent out. No way could I have done that had I stayed at uni.
That job led to another, which led to another, and 11 years on I am now working for myself doing what I love, comfortably supporting our family of four, knowing that leaving uni was one of the best decisions I ever made.
It's not for everyone - and your son leaving doesn't make him a failure - there's no reason he couldn't make it for himself if he wanted to enough - it's only a bit of paper at the end of the day.
It's important to note that my parents were behind me all the way through the decision I made as although they had expected me to go to uni, they realised it wasn't for me - so the more you are behind your son and understand and reassure him that you are behind whatever decision he makes, it will help no end.
Hope this helps!