I see that you earlier mentioned the Declaration of Independence. Given your statement above, maybe it will help to point out that the Declaration Of Independence states,
“We hold these Truths to be self-evident, that all Men are created equal, that they are endowed, by their CREATOR, with certain unalienable Rights, that among these are Life, Liberty, and the Pursuit of Happiness.–That to secure these Rights, Governments are instituted among Men…”
So the Supreme Court is not charged with securing those rights, it is The Government, of which the SC is one of three branches: Presidential, Legislative, and Judicial. Congress is the branch charged with making those laws. The role of (ordinary) judges is to hand down rulings based on the law. At times, the Supreme Court may be asked to review whether the laws passed by Congress and applied by judges are in accordance with the U.S. Constitution.
There have been bad SC judgements handed down over the decades. There will, no doubt, be more in the future. A lot of people would say that the SC’s recent ruling regarding Eminent Domain was ill-considered.
I think the basic difference to point out, based on your post, is that the U.S. is a country of laws, not men. A dictatorship, as has been pointed out by others, is the rule of the whim of man. A particular man. (Or woman.)
If we don’t like the laws are how they are applied we can vote the men and women who happen to be in power out of office. Not so with a dictator.
I don’t know if that helps, but I hope it does. A lawyer or Constitutional scholar can, I’m sure, offer a better description.