I'm reminded of H.P. Lovecraft: that we live on a placid island of ignorance in the midst of black seas of infinity, and it was not meant that we should voyage far. There's a lot not to like about Lovecraft but I think he pegged humanity's role in the cosmic order pretty well (we wouldn't have one.)

Any species capable of reaching our planet from another galaxy will be more than advanced enough to wipe us out without effort. If there's any sort of competition for resources or territory between aggressive civilizations operating at that scale and we find ourselves in the middle, we just lose. Our "fighting" them would be akin to termites "fighting" a steamroller flattening their mound.

The way I see it, conflict usually comes from means of profit, and limited resources. The universe is pretty damn big, and chances are once we're advanced enough to do space travel, there aren't going to be many resources in one place but not the other.

Conflict may also come from misunderstanding. Imagine a civilization where individuals are blobs of goo, and their way to understand each other and procreate/mutate is to mix with each other. Now if they would encounter a human being and realize that it's sentient, they would try to understand it by trying to mix as they usually do. From human's perspective that would be an act of violence and would prompt immediate defense/offense.