If ultra-advanced space aliens can hide large spacecraft from the Earth's population, and also do whatever it is they do without having a noticeable effect on Humanity, then, well - I say _let them_.

Either it's all just a collection of circumstantial mis-understandings and mis-interpretations, or at some point they'll do something we notice. Just don't worry about it.

Remember civilization is in grave danger regardless of that from global warming, running out of non-renewable resources, and last but not least nuclear war. Try to focus on making sure the aliens still have people to mess with...