I'm not embracing relativism. I'm not trying to get into individual issues (like abortion) I'm just offering them as a various problems that face the world today. I think abortion is wrong, I think it is murder. BUT, I wouldn't support invading conneticut or California because they pass laws supporting it. The United States government does not have that authority. I am against Sodomy and homosexual marriages, I think it is immoral, I think it spreads disease, etc. but I am against any Federal amendment making marriage between a man and a woman, this is also not something the Federal government has any business in.
I am for prayer in school, football games and public events, BUT I am against the Federal government coming in and telling a state that says I can't pray that they have to let me do it because they have something called the 14th amendment. (whether you agree with me on these issues or not isn't the point, you likely don't, but I am using them to illustrate where I am coming from in the topic of this thread)
As said, it would be (and has) creating a bigger monster than whatever said state or community is doing.
As far as historical issues you are trying to take complicated issues and people and oversimplify them.
Since you think we should be a centralized homogenous nation (you said you have no problem invading states within the United States), I would ask why you wouldn't support invading said countries to solve these problems. I mean, from your line of thinking, if something is wrong, then it's wrong and must immediately made right. All it takes is a gun, a few burned cities and slaughtered people in war and a law in the books and voila, instant equality, liberty and harmony. If centralization is good for America, why not extend that to the rest of the world? If moral change can only come from some mystically all knowing all powerful central government in these United States, then what are we waiting for? (wait! We aren't....we are doing it in Iraq, we tried it in Kosovo, in Serbia, in Haiti, in Vietnam, in the Phillipines, etc.)
I maintain that the Federal...or Central (nothing federal about it anymore) government has created FAR more problems than it has solved over the past 100 years or more because of the powers it has seized in the name of "equality" or "freedom" or "fairness."
I'll let Lord John Action, who also said "power corrupts and absolute power corrupts absolutely" tell it like it is as he did in a letter to Robert E. Lee after the War:
Without presuming to decide the purely legal question, on which it seems evident to me from Madison's and Hamilton's papers that the Fathers of the Constitution were not agreed, I saw in State Rights the only availing check upon the absolutism of the sovereign will, and secession filled me with hope, not as the destruction but as the redemption of Democracy. The institutions of your Republic have not exercised on the old world the salutary and liberating influence which ought to have belonged to them, by reason of those defects and abuses of principle which the Confederate Constitution was expressly and wisely calculated to remedy. I believed that the example of that great Reform would have blessed all the races of mankind by establishing true freedom purged of the native dangers and disorders of Republics. Therefore I deemed that you were fighting the battles of our liberty, our progress, and our civilization; and I mourn for the stake which was lost at Richmond more deeply than I rejoice over that which was saved at Waterloo.