I think it's important to note that we aren't immediately attacked by Thargoids. I know there are distress calls that show ships ravaged by what looks like Thargoid technology. However, every interaction i'm aware of from players has been benign. Maybe for gameplay purposes this has to be done, but a part of me thinks Frontier Developments wants us to believe that Thargoids are complicated and have priorities that are much different than anything humans care about.
Another thing to note is that we're seeing crashed Thargoid ships just a little too often for comfort. There's evidence that the Thargoids are under some kind of duress. These new sites are most definitely crashed Thargoid constructs. The "scavengers" at these sites, the fact Thargoid flower ships appear and scan the site and fly off, tell me there's something else at play here and there's at least enough evidence to make players wonder if this biological race is not at the top of the food chain.
It's important to also realize that extra terrestrial intelligence isn't "evil". There is emotional depth to organic intelligent life. Something that can create interstellar ships, operate insterstellar technology has to be enlightened to the point where I can't imagine Thargoids just magically appear as the big bad guy in 2.4 without a good reason, that may not even be the Thargoid's fault. It's also important to note just how HUGE the Galaxy is, so I can't imagine some incursion based on territory either.
Personally I'm siding with others who are laying claim to what I think is likely the underlying evil and that's the Monolith Network. A.I. is such a hot topic in today's world, and I think Frontier could probably tell a story about another civilizations A.I. destroying that civlization and hunting down the surviving organic "bioweapons" who are simply trying to survive and build a civilization for themselves. I'm all about the conspiracy theory that certain human superpowers like the federation and empire have somehow activated the monolith network, or the monolith network has somehow infiltrated the upper echelons of human society over time.
I was in the Thargoids are victims of something more dangerous camp 6 months ago, and nothing has changed my mind today. No matter how imposing they are, and regardless if we are going to be fighting them in the next patch. The fact that the Thargoids are a 2.4 patch not a 3.0 release tells me that they are actually the precurser to something else, if I'm reading the tea leaves. I bet just like Frontier has been leading players along a journey to their discovery, they will lead cannon and other researchers on another mystery into much deeper origins of 2.4's Thargoid conflict. Just my two cents with my tinfoil cap.