Then we find out that we just attack an alien messanger and because of our violent warlike ways,
Defending ourselves does not make us violent or warlike.
Humanity will be exterminated to prevent us exporting our violence to the rest of the galaxy.
If aliens really used this reasoning, the irony would almost be too much. "Let's stop violence by committing one of the most horrible violent acts (genocide) imaginable!"
It would also be a good example that just because you are capable of building advanced technology, doesn't mean you are intelligent.
I dont think these are hostile. similar UFO designs have been observed for a while now and non of them have carried out any attacks.
One does not have to attack to be considered hostile. The fact that they feel they can have free run of our planet without our permission could certainly be construed as hostile intent, even if they have no plans to actually attack us. Plus, if alien abduction stories are to be believed, I would say kidnapping and unlawful imprisonment of our citizens would certainly fall within the realm of "attack" and would be a clear display of hostile intent. At the very least, it is a violation of our sovereignty, which here on Earth is considered an act of war.
Why do you think aliens have a concept of "territory"? In order to have a concept of territory, you need to have a concept of materialism. You also need to have a concept of ownership. It is also not implied that any trespassing of "owned territory" is necessarily violation, that is also your implication. What if they never even had to struggle for ressources - What if, just due to the nature of their environment, they have been in a post-scarcity scenario from the get-go?
What their cultural and societal norms are, are completely irrelevant because they are visiting our world. As such, it is not unreasonable for us to expect aliens to abide by our customs and not offend us. It's kind of like when you visit another country, you are expected to adjust to and abide by their laws, society, and culture because you are the outsider and have no right to impose your own ways on them. If these hypothetical aliens were really as intelligent as people seem to think they would be, you'd think they'd have the good sense to study our society from a distance first to learn how to not offend us and then take the proper steps diplomatically to avoid any unfortunate incidents between our civilizations.
You are just anthropormphising for no good reason.
Actually, there's a very good reason to anthropomorphize. I stated it above. They are the ones visiting our world. The means it is their responsibility to abide by our laws, customs, and societal norms if they wish to operate here unmolested. We, as the native inhabitants of this world, have no obligation to accommodate the aliens or their culture. So if they have no concept of territory or sovereignty, they better learn real quick if they don't want one of their scientists or diplomats getting shot down and killed/captured.
Much like a human pouring hot water over an ant nest wouldn't be the ant's fault, but at the same time you can't really expect humans to try to talk to ants before they build a new subdivision.
This isn't a very good analogy. A better analogy would be how modern societies send researchers to study some of those primitive tribes still living in the Amazon or in the South Pacific. Some of those tribes are openly hostile when their territory is encroached upon, and rightfully so. Would you advocate sending in the full might of the US military if one of those tribes captured and killed some university professor that decided to get too close to one of those hostile tribes? No, you wouldn't because that would be a completely unreasonable response to a society just trying to protect itself from an unknown threat.