Yes, but this logic does not apply to MU. If so, all villains should also be fighting Knull (or any other worldwide threat), but that never happens. Likewise anti-mutant activists do not make protests against Avengers and FF, their agenda is to eliminate mutants and not face the threats of everyday life.
Russia, for example, is a declared anti-Krakoa country. Suppose Krakoa opens its gateways across the globe, what prevents Russians from sending spies or sleeping agents? Or even other countries that just approved the agreement, but do not necessarily approve the new nation? Professor X and Magneto speak not only for a group of 30/50 trained mutant heroes, but for hundreds of mutants who have spent their lives away from combat or conflict. Krakoa IS NOT the Xavier Institute.
AND AGAIN, the gateways are organic, a physical part of Krakoa, all connected to the island's consciousness, and only Krakoa can previously grant access through them. The entire Quiet Council can argue with him, but I doubt that he will grant access to humans who offer him nothing in return, other than threats.
And by the way, if Krakoa opened its gateways to the whole world, I think it would be IMPOSSIBLE GEOGRAPHICALLY SPEAKING to accommodate the whole world on an island.