I feel kids are confident in their independence when they choose to do it themselves rather than pushing.
You're a savvy adult, and small children are easy to manipulate. I'm sure you can find a want to make him want it and think it was his idea all along. Talk up about how awesome being a big kid is and how big kids go to school alone. When he suggests he go in alone, tell him what a wonderful idea it is, if you really insist on mollycoddling your child.
Going on my own experiences the more I was pushed the more I dug my heels in. When I was left to grow at my own rate it was much better
Yeah... Sometimes that works. Sometimes you get 40 year old still living in the basement mooching off mom and dad. Kind of a crap shoot on that one.
Independence is expected, and it needs to be made clear to them.
There's lots of things kids don't like doing that you make them do anyway for their own good: Wearing seat belts, eating healthy, wearing a bike helmet, holding your hand when crossing the road, getting immunizations.
How is this any different? Kids are too short sighted to understand that temporary unhappiness will eventually have long term benefits.
Teaching him that he is expected to go in alone, and that school is non-negotiable is only setting him up for success. There will be lots of things he doesn't want to do in life, teach him skills to cope with that while he's young.