makes sense and if the federation is more like the EU than the United states then maybe they are not as involved the in the internal politics and cultures of member states, just as long as they meet certain aspects of laws that are considered universal for membership into the federation. Maybe democracy, separation of state and religion etc.Vulcan isn't a free society, though - it's apparently forbidden to speak of pon farr. This would no doubt be a condition placed upon all those living on Vulcan, too. One doesn't get all that far in the US by insisting that kids are valid sex partners or cocaine is good for your brain - there are certain limits to freedom that a multicultural entity like the UFP would be constantly banging its head against, and by definition many of those would appear absurd to parties other than the one involved.
Or it could just be that as a founding member vulcan had special exemptions because the federation was not strong enough at the time to force certain idealogies on vulcans, unlike now that it seems very powerful and wont permit new members from carrying on certain customs that they might have overlooked when they where first starting.