I've had mixed emotions over this one, but I can't say that I ever "mourned" about it. I really loved the infant and toddler years with both of my kids and felt a little sad that the days without school structure and homework were at an end. Once they got into school (for me), it became a much more hustle and bustle schedule. And yes... in our (public) school, there is already homework and projects in kindergarten.
My youngest was so ready in so many ways to move one to something else that it didn't seem as hard to let him go into kinder. And he's got a much more outgoing personality than my (eldest) daughter, so he wasn't clinging to me at the door in the mornings.
Now that they are both in school, I cherish the time off for winter break, spring break, summer vacation etc... and I love watching them grow into this new phase of childhood. I like hearing about the new things they are learning and doing, seeing their confidence grow, hearing about new friends they are meeting.
It sounds like your husband is the one who is really sad about your little guy "growing up" and going to school and is projecting that onto you. I'd talk to him about it... he may also be trying to be sympathetic to how you might be feeling about it, not realizing your position on it. Actually, I think it's pretty sweet and sensitive of him.
Good luck!