From a sovereignty perspective, does a launch from continental Europe actually matter when Arianespace/CNES/ESA has been launching from France for decades?
Regardless, a launch facility within Europe seems much less riskier long term from a geopolitical standpoint.
Yes, that's why the risk is NOT the same between French Guiana and New Caledonia. Both of them are oversea territories far from the mainland with a colonial past, but their current relationship with the mainland is very different.
Around a quarter of the population of New Caledonia has been calling for independence for decades at this point, with 3 referendum organised during the last 10 years to resolve this issue. Only half of the population was able to vote to the referendums (and some local elections, like Congress of NC), due to local rules than are about to change–this, incidentally, is the cause of the protests you are talking about. On the geopolitical side of things, the independentists are probably propped up by Azerbaijan (https://www.courrierinternational.com/article/geopolitique-n...) and maybe China (https://www.lefigaro.fr/international/ambitions-geostrategiq...).
None of this holds for French Guiana. The risk between these territories is not the same. At all. Putting them on the same level by reducing them to their status as former colonies is nonsense.
Sure, placing launch infrastructure in French Guiana is probably less risky than setting up shop in New Caledonia. Clearly, the risk profile is not the same for all of Overseas France.
My point is that if the decision is between mainland and Overseas France, the latter introduces elevated risk in the long term in general. French Guiana could be fine today, but it is not impossible that the next few years could see the rise of a populist pro-independence movement that would eventually impact launch infrastructure (similar to how it did for the USSR).
Reality is fundamentally chaotic after all.
https://en.wikipedia.org/wiki/SaxaVord_Spaceport
How about the last time South America contested a little parcel of land?
My opinion is that there is an implied reliance on the US "allowing" Europe to ship the rockets to Kourou and launch them there.
If our relations ever completely sour, the US might, for example, take over the shipping vessels going to Kourou, kinda like Europe takes over Russian shadow fleet vessels.
Now all of a sudden Europe has no means of launching rockets, except now it can launch to polar orbits. It might seem a stretch, but there is a non-zero chance that could happen, therefore it is better to have an alternative.
No, but it makes it vulnerable to the US.
The US can also decide to “free” and “bring democracy” to the French Guiana because the rich oil deposits of its continental shelf won’t free themselves.
The point is that a slow ship crossing the ocean with hard to replace is very vulnerable in transit.
Though not every sovereign state has an army, see Iceland, Costa Rica, theoretically Japan, etc.