How is it any different? USA and Europe are roughly comparable as a group of states that unite together under some common rules (EU does have some common rules and it has its own leaders). The two are about the same physical size with a similar population and a similar amount of diversity between all of the member states. Saying all Americans should fall under the same rules is on the same level of crazy as saying all of Europe should have exactly the same rules. Ron Paul seems to realize that it's silly to expect a group that large and that diverse to all agree to the same things. It just isn't going to work. California and Texas may be right next to each other, but they're nothing alike. They're about as different as Britain and France. Even the populations in those two states rival the populations of other countries. California and Canada have roughly the same population.
Try to think in terms of why USA was started. You have 13 colonies. All of them are weak, and relations are a bit rocky with big and powerful Britain. None of the colonies stand a chance against Britain, but together it's a bit more even. It would make sense to unite all of them for a common goal. It's the same idea as NATO or the Warsaw Pact. A shared currency might help as well.... sort of like the Euro. That should be the end of it. Shared army, shared currency, shared federal taxation (to pay for the shared army), and that's it. Forcing California and Texas to have the same laws is asking for trouble. One is very anti-gun, the other is pro-gun. One is anti-gay, the other is simply gay. That's all fine. If you're gay, you go to the gay state. If you hate gays, feel free to leave and go to the anti-gay state. Banning gay marriage will anger 30 million people, but allowing it will anger 30 million other people. Forcing the same rules on everyone causes everyone to lose at some point. People in California might think forcing civil rights on the south was a success, but the south thinks that shutting down marijuana clinics in California is a success. This is failure at its finest. The whole country is divided on nearly every issue. How many times do people in here say California should just break off and leave the union? Guess why that is.
No problem. Change the constitution and you're good to go. That's what Bush was trying to pull with his gay marriage thing. There's also a nation wide ban on stem cell research (I think).
In any event, Ron Paul is only fooling himself if he thinks the civil war could be avoided by buying slaves. Slaves are not just "things" you can buy out. They were farm equipment. They were industrial machines. They drove the economy. Slavery was why the south could sell things at low costs and remain competitive. Outlawing it or trying to buy them out is like trying to outlaw or buy out industrial machinery. Yeah they get a lump sum payment, but what happens when industry falls on its face? They.... go back to Africa and get more slaves. Duh. If you buy the car I need to get to work, then obviously I'll go find another car to get the same work done.
The war had less to do with moral highground and more to do with not being able to compete. The guys in the north are like modern Americans with high wages. The slaves in the south are like modern Chinese workers. With costs that low, industry heads south.