I have a few thoughts here. First of all, I think your husband is kind of viewing this from an adult perspective, not from the perspective of a child who has been in the same bedroom for his/her whole life. Yes, as an adult (or even an older child), if you were suddenly told "here is your bedroom. It's the smallest," you'd probably feel cheated. But if you had the same bedroom your whole life, that would just seem normal. You wouldn't wake up one day and be like, "What the crap?? Why is my bedroom so small?" As a teen, it might occur to you to be mad that your room was so small, but teens get mad about random things anyway.
Secondly, yes, I shared a bedroom with my sister, and it sometimes sucked and I wanted my own room. My brother (youngest sibling) had his own room because he was the only boy, and my sister and I would periodically wish that we had our own room, but since he was the only boy, it was just the way it was. Ironically, he used to complain that my sister and I "got to" share a room while he had to sleep in a room all by himself. So there's really no predicting how a child is going to feel about sharing a room versus having his/her own space.
If room size is literally the only thing keeping you from having another child, I honestly think it's a dumb reason not to have a kid.
ETA - Oh, I just read that you weren't considering not having a child because of the room situation. Disregard my last sentence.