Bob Lazar goes on record to recount his experiences at the S4 Facility, Groom Lake, Nevada. He has passed two lie detector tests about his experiences, so he is either telling the truth or he is the greatest actor who ever lived. I am not the Lyra I am the song.
The Zetas are one of few races in a worse situation than humanity. By example we can still reproduce naturally. They cannot: they just clone themselves. I have great sympathy for their kind & I can understand the beliefs that sponsor their actions: unfortunately for all of us they broke the Rulz: (no typo) Let each soul go their own course. In doing so they took advantage of the human thirst for power & many years ago nearly doomed us all to their own fate. Research Dows, Dals, Zeta 1 & 2, Alex Collier & the book Gods of Eden by William Bramley.
They're not necessarily evil, they have a balance of gifts and turmoil just as we do. It's my view that they're just trying to save their kind. However there are many species of Zetas and while most of them are benevolent, some are not. They are also, like most of who's out there, both physical and non-physical beings - extremely spiritual.