If the Thargoid we see in game were actively hostile to humanity, they would, well, be actively hostile.
Instead, I can pop into any number of non-human signal sources and the Thargoid will come over, scan me, and then just ignore me.
Given the relative power imbalance we've been told of, the human death toll would be far, far higher well.
The reality is, we do not know what the Thargoids consider hostile to them. We only know what we consider hostile to us. We can't assume they have a human mind and the two understandings of hostility are comparable.
We see ships, megaships, and stations attacked by them, yes. We do not know why they attacked. So it's incorrect to assume that we therefore do know, and the answer is malice - there are also many un-attacked ships, megaships, and stations, even in the Pleiades.
People who claim the Thargoids are hostile to humanity ignore some very simple facts: A Thargoid will come up to my ship, scan it, and leave. I am a human. That was not hostile. The logical conclusion is Thargoids are not hostile to all humans.
We should be focusing our efforts to determine what the trigger point is that makes them hostile. The only triggers that turn them hostile that I've observed are hostility, carrying their tech and not releasing it (and the period between "carrying" and "not releasing" reaffirms their non-hostile intent), and carrying Guardian tech.
This implies they are apparently hostile in reaction to hostility, theft/kidnapping/dissection (depending how they define us taking their artifacts), and Guardians. Not "humans" in a general sense, but "humans who do these things".