The negative groups have STILL not realized that they are only able to do what they are ALLOWED to do.
In order to answer the question of "who allows them," it is ultimately necessary to break through into at least some minimum grade of understanding regarding the fact that Earth is a laboratory for spiritual growth.
Beings with capabilities far vaster than any ETs we might normally think of are making sure that we are never offered more on Earth than what we are creating. In that sense the world becomes a perfect mirror for our own collective disharmony.
It certainly appears as if everything you're seeing, hearing and reading about is a story that is "out there," and has no direct significance to your own life. This is the illusion.
The reality is that the world is offering us precisely what we need to be awakened -- on a mass, worldwide level. You can dislike the process, but we're not at a level where we have any direct say in whether it works this way.
That means the greater objective is to understand the process, and understand that you, right now, reading this, have far more control over the outcome than you may have ever realized.