There must be reasons they're using these words. Whether those reasons come to fruition or not is another argument.

Your role as BBS Grammarian is causing you to read way too much into these terms. Sovereign is rarely used with the connotation of "supreme power" or "unlimited in extent." I've always taken it to mean self-governing and autonomous, but not necessarily in the belligerent manner that you seem to be implying. Sometimes, a cigar is just a cigar.

The supposed rationale for entering Iraq were those ``substantial consequences''. But those were provided for (albeit not specifically) by the UN, not by the US's supreme right.

And the U.N. was not going to enforce those serious consequences. Ever. France would not pass any resolution that held Saddam accountable. So they were refusing to enforce the serious consequences. If anything, the U.S. is the one making sure that the letter and spirit of the existing U.N. resolutions were followed, damn the French and their desire to protect their economic interests.

Edit: More French arrogance.
But asked by The Telegraph whether he hoped American and British forces would win the military campaign to remove Saddam Hussein, he replied angrily: "I'm not going to answer. You have not been listening carefully to what I said before. You already have the answer."
...
Embarrassed French officials tried to salvage the situation by pointing out that, on French television on Monday, M de Villepin said: "Clearly, we hope the US will win this war quickly."
...
Moreover M de Villepin did himself few favours with Washington when, recalling the "bleakest time in our history" during the Second World War, he extolled Winston Churchill and Charles de Gaulle but left out Franklin D Roosevelt's role in the liberation of France.