[BroJoeK]

"The closer to the equator you launch from, the more assist you get from the Earth's rotation."

Sure, but the distance from Cape Canaveral to French Guiana is only 1600 miles in latitude.
If it were that important, why not launch from, say, Hawaii's big island, only 1,000 miles north in latitude from French Guiana?

Not saying French Guiana isn't a good idea, but if there are unnecessary risks, why take them?

[Yo-Yo]

Sure, but the distance from Cape Canaveral to French Guiana is only 1600 miles in latitude.

If it were that important, why not launch from, say, Hawaii's big island, only 1,000 miles north in latitude from French Guiana?

The European Space Agency launch facility Guiana Space Centre is at 5° 13' 53" N, whereas the southernmost point of the Hawaiian Island chain is at 18° 58' 3" N, plus just think of the shipping time from anywhere in the Gulf of Mexico to Hawaii.

Impractical.