According to your other post, your husband was bullied as a kid. So if this is a true story and not a research project, then why WOULDN'T he feel that children shouldn't be made to get along? What if someone had told him that he had to be friends with the kid who tormented him?
Instead of trying to make everything roses, why don't you consider that you don't get to "fix" everyone around you? If kids don't get along, there's a reason. You can only work on the reason on your own side of it. You can't work on the reason for the other kid - it's not your place. And your child has the right to not care for another kid's personality.
Yes, little kids fighting over a toy need to learn to play together. It's not about them "settling their differences". Up til a certain point, it's the adults in their lives that help them learn to share, to not fight, etc. There's parallel play for the younger set, playing together where children have equal footing when they're a little older, and then by the time they are really old enough to have an opinion, they choose their friendships. For the kids who tend to bully and call all the shots, it's the adult's responsibility to prevent that. When they don't, the other child should have the right to say "I don't want to play with him." Let it be.