If they wanted to harm us, it would be a very short war.
All they would have to do, is drop some rocks on us. With asteroid belts on either side of our planet, it wouldn’t require very many, or a whole lot of effort on their part; and there isn’t a damn thing we could do about it.
If they wanted to KILL us, it would be a very short war.
Whitley Strieber (a well-known contactee and author of the book Communion) says that what the so-called aliens want is to experience life on this planet by sharing our minds, bodies, and souls with us. A kind of cohabitation.
He speculates (rightly or wrongly) that they are not physical as we are and are rather devoid of emotions and senses. They can't live on this planet in their current form and need our permission to indwell us and enjoy life on this beautiful planet as we experience it.
As an aside, the reason these beings need our permission is that without it they would only inhabit a completely freaked-out and depressed person and that defeats the purpose of the co-habitation.