We are following Luffy's adventures but we should never forget most pirates are like Vasco Shot or Kid. Thieves, murderers, rapists, the worst society has to offer. The WG exist to keep them at bay and protect the world.
Also secrets can be extremely dangerous. Should the Ancient weapons be awakened, tens of thousands would die, chaos would spread and the strongest pirates would rule the world as they like.
Why shouldn't they trust the government? It is trying his best, isn't it?