You have it backwards. ET's are already here.
Negative ET's have been here for thousands of years running the world from the shadows.
They have enslaved humanity.
Positive ET's want to help however the negative ET's control the world leaders and media.
If the positive ET's come to help the people will freak out because they have been conditioned for an "invasion" If they come to help the puppet world leaders will attack them with the full might of the worlds military powers,
The sheep will cheer and scream "KILL THEM ALL!", the positive aliens would have to defend themselves. The negative alien's would sit back and laugh their asses off.
So what do you do?